This manual describes how to install, use and extend NixOS, a Linux distribution based on the purely functional package management system Nix, that is composed using modules and packages defined in the Nixpkgs project.

Additional information regarding the Nix package manager and the Nixpkgs project can be found in respectively the Nix manual and the Nixpkgs manual.

If you encounter problems, please report them on the Discourse or on the #nixos channel on Freenode. Bugs should be reported in NixOS’ GitHub issue tracker.

Note: Commands prefixed with # have to be run as root, either requiring to login as root user or temporarily switching to it using sudo for example.

This section describes how to obtain, install, and configure NixOS for first-time use.

Chapter 1. Obtaining NixOS

NixOS ISO images can be downloaded from the NixOS download page. There are a number of installation options. If you happen to have an optical drive and a spare CD, burning the image to CD and booting from that is probably the easiest option. Most people will need to prepare a USB stick to boot from. Section 2.5.1, “Booting from a USB Drive” describes the preferred method to prepare a USB stick. A number of alternative methods are presented in the NixOS Wiki.

As an alternative to installing NixOS yourself, you can get a running NixOS system through several other means:

  • Using virtual appliances in Open Virtualization Format (OVF) that can be imported into VirtualBox. These are available from the NixOS download page.

  • Using AMIs for Amazon’s EC2. To find one for your region and instance type, please refer to the list of most recent AMIs.

  • Using NixOps, the NixOS-based cloud deployment tool, which allows you to provision VirtualBox and EC2 NixOS instances from declarative specifications. Check out the NixOps homepage for details.

Chapter 2. Installing NixOS

2.1. Booting the system

NixOS can be installed on BIOS or UEFI systems. The procedure for a UEFI installation is by and large the same as a BIOS installation. The differences are mentioned in the steps that follow.

The installation media can be burned to a CD, or now more commonly, "burned" to a USB drive (see Section 2.5.1, “Booting from a USB Drive”).

The installation media contains a basic NixOS installation. When it’s finished booting, it should have detected most of your hardware.

The NixOS manual is available on virtual console 8 (press Alt+F8 to access) or by running nixos-help.

You are logged-in automatically as nixos. The nixos user account has an empty password so you can use sudo without a password.

If you downloaded the graphical ISO image, you can run systemctl start display-manager to start the desktop environment. If you want to continue on the terminal, you can use loadkeys to switch to your preferred keyboard layout. (We even provide neo2 via loadkeys de neo!)

2.1.1. Networking in the installer

The boot process should have brought up networking (check ip a). Networking is necessary for the installer, since it will download lots of stuff (such as source tarballs or Nixpkgs channel binaries). It’s best if you have a DHCP server on your network. Otherwise configure networking manually using ifconfig.

To manually configure the network on the graphical installer, first disable network-manager with systemctl stop NetworkManager.

To manually configure the wifi on the minimal installer, run wpa_supplicant -B -i interface -c <(wpa_passphrase 'SSID' 'key').

If you would like to continue the installation from a different machine you need to activate the SSH daemon via systemctl start sshd. You then must set a password for either root or nixos with passwd to be able to login.

2.2. Partitioning and formatting

The NixOS installer doesn’t do any partitioning or formatting, so you need to do that yourself.

The NixOS installer ships with multiple partitioning tools. The examples below use parted, but also provides fdisk, gdisk, cfdisk, and cgdisk.

The recommended partition scheme differs depending if the computer uses Legacy Boot or UEFI.

2.2.1. UEFI (GPT)

Here's an example partition scheme for UEFI, using /dev/sda as the device.

Note: You can safely ignore parted's informational message about needing to update /etc/fstab.

  1. Create a GPT partition table.

    # parted /dev/sda -- mklabel gpt

  2. Add the root partition. This will fill the disk except for the end part, where the swap will live, and the space left in front (512MiB) which will be used by the boot partition.

    # parted /dev/sda -- mkpart primary 512MiB -8GiB

  3. Next, add a swap partition. The size required will vary according to needs, here a 8GiB one is created.

    # parted /dev/sda -- mkpart primary linux-swap -8GiB 100%

    Note: The swap partition size rules are no different than for other Linux distributions.

  4. Finally, the boot partition. NixOS by default uses the ESP (EFI system partition) as its /boot partition. It uses the initially reserved 512MiB at the start of the disk.

    # parted /dev/sda -- mkpart ESP fat32 1MiB 512MiB
    # parted /dev/sda -- set 3 boot on

Once complete, you can follow with Section 2.2.3, “Formatting”.

2.2.2. Legacy Boot (MBR)

Here's an example partition scheme for Legacy Boot, using /dev/sda as the device.

Note: You can safely ignore parted's informational message about needing to update /etc/fstab.

  1. Create a MBR partition table.

    # parted /dev/sda -- mklabel msdos

  2. Add the root partition. This will fill the the disk except for the end part, where the swap will live.

    # parted /dev/sda -- mkpart primary 1MiB -8GiB

  3. Finally, add a swap partition. The size required will vary according to needs, here a 8GiB one is created.

    # parted /dev/sda -- mkpart primary linux-swap -8GiB 100%

    Note: The swap partition size rules are no different than for other Linux distributions.

Once complete, you can follow with Section 2.2.3, “Formatting”.

2.2.3. Formatting

Use the following commands:

  • For initialising Ext4 partitions: mkfs.ext4. It is recommended that you assign a unique symbolic label to the file system using the option -L label, since this makes the file system configuration independent from device changes. For example:

    # mkfs.ext4 -L nixos /dev/sda1

  • For creating swap partitions: mkswap. Again it’s recommended to assign a label to the swap partition: -L label. For example:

    # mkswap -L swap /dev/sda2

  • UEFI systems

    For creating boot partitions: mkfs.fat. Again it’s recommended to assign a label to the boot partition: -n label. For example:

    # mkfs.fat -F 32 -n boot /dev/sda3

  • For creating LVM volumes, the LVM commands, e.g., pvcreate, vgcreate, and lvcreate.

  • For creating software RAID devices, use mdadm.

2.3. Installing

  1. Mount the target file system on which NixOS should be installed on /mnt, e.g.

    # mount /dev/disk/by-label/nixos /mnt

  2. UEFI systems

    Mount the boot file system on /mnt/boot, e.g.

    # mkdir -p /mnt/boot
    # mount /dev/disk/by-label/boot /mnt/boot

  3. If your machine has a limited amount of memory, you may want to activate swap devices now (swapon device). The installer (or rather, the build actions that it may spawn) may need quite a bit of RAM, depending on your configuration.

    # swapon /dev/sda2

  4. You now need to create a file /mnt/etc/nixos/configuration.nix that specifies the intended configuration of the system. This is because NixOS has a declarative configuration model: you create or edit a description of the desired configuration of your system, and then NixOS takes care of making it happen. The syntax of the NixOS configuration file is described in Chapter 5, Configuration Syntax, while a list of available configuration options appears in Appendix A, Configuration Options. A minimal example is shown in Example 2.4, “NixOS Configuration”.

    The command nixos-generate-config can generate an initial configuration file for you:

    # nixos-generate-config --root /mnt

    You should then edit /mnt/etc/nixos/configuration.nix to suit your needs:

    # nano /mnt/etc/nixos/configuration.nix

    If you’re using the graphical ISO image, other editors may be available (such as vim). If you have network access, you can also install other editors — for instance, you can install Emacs by running nix-env -f '<nixpkgs>' -iA emacs.

    BIOS systems

    You must set the option boot.loader.grub.device to specify on which disk the GRUB boot loader is to be installed. Without it, NixOS cannot boot.

    UEFI systems

    You must set the option boot.loader.systemd-boot.enable to true. nixos-generate-config should do this automatically for new configurations when booted in UEFI mode.

    You may want to look at the options starting with boot.loader.efi and boot.loader.systemd as well.

    If there are other operating systems running on the machine before installing NixOS, the boot.loader.grub.useOSProber option can be set to true to automatically add them to the grub menu.

    If you need to configure networking for your machine the configuration options are described in Chapter 11, Networking. In particular, while wifi is supported on the installation image, it is not enabled by default in the configuration generated by nixos-generate-config.

    Another critical option is fileSystems, specifying the file systems that need to be mounted by NixOS. However, you typically don’t need to set it yourself, because nixos-generate-config sets it automatically in /mnt/etc/nixos/hardware-configuration.nix from your currently mounted file systems. (The configuration file hardware-configuration.nix is included from configuration.nix and will be overwritten by future invocations of nixos-generate-config; thus, you generally should not modify it.) Additionally, you may want to look at Hardware configuration for known-hardware at this point or after installation.

    Note: Depending on your hardware configuration or type of file system, you may need to set the option boot.initrd.kernelModules to include the kernel modules that are necessary for mounting the root file system, otherwise the installed system will not be able to boot. (If this happens, boot from the installation media again, mount the target file system on /mnt, fix /mnt/etc/nixos/configuration.nix and rerun nixos-install.) In most cases, nixos-generate-config will figure out the required modules.
  5. Do the installation:

    # nixos-install

    This will install your system based on the configuration you provided. If anything fails due to a configuration problem or any other issue (such as a network outage while downloading binaries from the NixOS binary cache), you can re-run nixos-install after fixing your configuration.nix.

    As the last step, nixos-install will ask you to set the password for the root user, e.g.

    setting root password...
    Enter new UNIX password: ***
    Retype new UNIX password: ***

    Note: For unattended installations, it is possible to use nixos-install --no-root-passwd in order to disable the password prompt entirely.

  6. If everything went well:

    # reboot

  7. You should now be able to boot into the installed NixOS. The GRUB boot menu shows a list of available configurations (initially just one). Every time you change the NixOS configuration (see Changing Configuration ), a new item is added to the menu. This allows you to easily roll back to a previous configuration if something goes wrong.

    You should log in and change the root password with passwd.

    You’ll probably want to create some user accounts as well, which can be done with useradd:

    $ useradd -c 'Eelco Dolstra' -m eelco
    $ passwd eelco

    You may also want to install some software. For instance,

    $ nix-env -qaP \*

    shows what packages are available, and

    $ nix-env -f '<nixpkgs>' -iA w3m

    installs the w3m browser.

2.4. Installation summary

To summarise, Example 2.3, “Commands for Installing NixOS on /dev/sda shows a typical sequence of commands for installing NixOS on an empty hard drive (here /dev/sda). Example 2.4, “NixOS Configuration” shows a corresponding configuration Nix expression.

Example 2.1. Example partition schemes for NixOS on /dev/sda (MBR)

# parted /dev/sda -- mklabel msdos
# parted /dev/sda -- mkpart primary 1MiB -8GiB
# parted /dev/sda -- mkpart primary linux-swap -8GiB 100%

Example 2.2. Example partition schemes for NixOS on /dev/sda (UEFI)

# parted /dev/sda -- mklabel gpt
# parted /dev/sda -- mkpart primary 512MiB -8GiB
# parted /dev/sda -- mkpart primary linux-swap -8GiB 100%
# parted /dev/sda -- mkpart ESP fat32 1MiB 512MiB
# parted /dev/sda -- set 3 boot on

Example 2.3. Commands for Installing NixOS on /dev/sda

With a partitioned disk.

# mkfs.ext4 -L nixos /dev/sda1
# mkswap -L swap /dev/sda2
# swapon /dev/sda2
# mkfs.fat -F 32 -n boot /dev/sda3        # (for UEFI systems only)
# mount /dev/disk/by-label/nixos /mnt
# mkdir -p /mnt/boot                      # (for UEFI systems only)
# mount /dev/disk/by-label/boot /mnt/boot # (for UEFI systems only)
# nixos-generate-config --root /mnt
# nano /mnt/etc/nixos/configuration.nix
# nixos-install
# reboot

Example 2.4. NixOS Configuration

{ config, pkgs, ... }: {
  imports = [
    # Include the results of the hardware scan.

  boot.loader.grub.device = "/dev/sda";   # (for BIOS systems only)
  boot.loader.systemd-boot.enable = true; # (for UEFI systems only)

  # Note: setting fileSystems is generally not
  # necessary, since nixos-generate-config figures them out
  # automatically in hardware-configuration.nix.
  #fileSystems."/".device = "/dev/disk/by-label/nixos";

  # Enable the OpenSSH server.
  services.sshd.enable = true;

2.5. Additional installation notes

2.5.1. Booting from a USB Drive

For systems without CD drive, the NixOS live CD can be booted from a USB stick. You can use the dd utility to write the image: dd if=path-to-image of=/dev/sdX. Be careful about specifying the correct drive; you can use the lsblk command to get a list of block devices.

On macOS

$ diskutil list
/dev/diskN (external, physical):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
$ diskutil unmountDisk diskN
Unmount of all volumes on diskN was successful
$ sudo dd if=nix.iso of=/dev/rdiskN

Using the 'raw' rdiskN device instead of diskN completes in minutes instead of hours. After dd completes, a GUI dialog "The disk you inserted was not readable by this computer" will pop up, which can be ignored.

The dd utility will write the image verbatim to the drive, making it the recommended option for both UEFI and non-UEFI installations.

2.5.2. Booting from the netboot media (PXE)

Advanced users may wish to install NixOS using an existing PXE or iPXE setup.

These instructions assume that you have an existing PXE or iPXE infrastructure and simply want to add the NixOS installer as another option. To build the necessary files from a recent version of nixpkgs, you can run:

nix-build -A netboot nixos/release.nix

This will create a result directory containing: * bzImage – the Linux kernel * initrd – the initrd file * netboot.ipxe – an example ipxe script demonstrating the appropriate kernel command line arguments for this image

If you’re using plain PXE, configure your boot loader to use the bzImage and initrd files and have it provide the same kernel command line arguments found in netboot.ipxe.

If you’re using iPXE, depending on how your HTTP/FTP/etc. server is configured you may be able to use netboot.ipxe unmodified, or you may need to update the paths to the files to match your server’s directory layout

In the future we may begin making these files available as build products from hydra at which point we will update this documentation with instructions on how to obtain them either for placing on a dedicated TFTP server or to boot them directly over the internet.

2.5.3. Installing in a VirtualBox guest

Installing NixOS into a VirtualBox guest is convenient for users who want to try NixOS without installing it on bare metal. If you want to use a pre-made VirtualBox appliance, it is available at the downloads page. If you want to set up a VirtualBox guest manually, follow these instructions:

  1. Add a New Machine in VirtualBox with OS Type "Linux / Other Linux"

  2. Base Memory Size: 768 MB or higher.

  3. New Hard Disk of 8 GB or higher.

  4. Mount the CD-ROM with the NixOS ISO (by clicking on CD/DVD-ROM)

  5. Click on Settings / System / Processor and enable PAE/NX

  6. Click on Settings / System / Acceleration and enable "VT-x/AMD-V" acceleration

  7. Click on Settings / Display / Screen and select VBoxVGA as Graphics Controller

  8. Save the settings, start the virtual machine, and continue installation like normal

There are a few modifications you should make in configuration.nix. Enable booting:

boot.loader.grub.device = "/dev/sda";

Also remove the fsck that runs at startup. It will always fail to run, stopping your boot until you press *.

boot.initrd.checkJournalingFS = false;

Shared folders can be given a name and a path in the host system in the VirtualBox settings (Machine / Settings / Shared Folders, then click on the "Add" icon). Add the following to the /etc/nixos/configuration.nix to auto-mount them. If you do not add "nofail", the system will no boot properly. The same goes for disabling rngd which is normally used to get randomness but this does not work in virtual machines.

{ config, pkgs, ...} :
  security.rngd.enable = false; // otherwise vm will not boot

  fileSystems."/virtualboxshare" = {
    fsType = "vboxsf";
    device = "nameofthesharedfolder";
    options = [ "rw" "nofail" ];

The folder will be available directly under the root directory.

2.5.4. Installing from another Linux distribution

Because Nix (the package manager) & Nixpkgs (the Nix packages collection) can both be installed on any (most?) Linux distributions, they can be used to install NixOS in various creative ways. You can, for instance:

  1. Install NixOS on another partition, from your existing Linux distribution (without the use of a USB or optical device!)

  2. Install NixOS on the same partition (in place!), from your existing non-NixOS Linux distribution using NIXOS_LUSTRATE.

  3. Install NixOS on your hard drive from the Live CD of any Linux distribution.

The first steps to all these are the same:

  1. Install the Nix package manager:

    Short version:

    $ curl | sh
    $ . $HOME/.nix-profile/etc/profile.d/ # …or open a fresh shell

    More details in the Nix manual

  2. Switch to the NixOS channel:

    If you've just installed Nix on a non-NixOS distribution, you will be on the nixpkgs channel by default.

    $ nix-channel --list

    As that channel gets released without running the NixOS tests, it will be safer to use the nixos-* channels instead:

    $ nix-channel --add nixpkgs

    You may want to throw in a nix-channel --update for good measure.

  3. Install the NixOS installation tools:

    You'll need nixos-generate-config and nixos-install and we'll throw in some man pages and nixos-enter just in case you want to chroot into your NixOS partition. They are installed by default on NixOS, but you don't have NixOS yet..

    $ nix-env -iE "_: with import <nixpkgs/nixos> { configuration = {}; }; with; [ nixos-generate-config nixos-install nixos-enter manual.manpages ]"
  4. Note: The following 5 steps are only for installing NixOS to another partition. For installing NixOS in place using NIXOS_LUSTRATE, skip ahead.

    Prepare your target partition:

    At this point it is time to prepare your target partition. Please refer to the partitioning, file-system creation, and mounting steps of Chapter 2, Installing NixOS

    If you're about to install NixOS in place using NIXOS_LUSTRATE there is nothing to do for this step.

  5. Generate your NixOS configuration:

    $ sudo `which nixos-generate-config` --root /mnt

    You'll probably want to edit the configuration files. Refer to the nixos-generate-config step in Chapter 2, Installing NixOS for more information.

    Consider setting up the NixOS bootloader to give you the ability to boot on your existing Linux partition. For instance, if you're using GRUB and your existing distribution is running Ubuntu, you may want to add something like this to your configuration.nix:

    boot.loader.grub.extraEntries = ''
      menuentry "Ubuntu" {
        search --set=ubuntu --fs-uuid 3cc3e652-0c1f-4800-8451-033754f68e6e
        configfile "($ubuntu)/boot/grub/grub.cfg"

    (You can find the appropriate UUID for your partition in /dev/disk/by-uuid)

  6. Create the nixbld group and user on your original distribution:

    $ sudo groupadd -g 30000 nixbld
    $ sudo useradd -u 30000 -g nixbld -G nixbld nixbld
  7. Download/build/install NixOS:

    Warning: Once you complete this step, you might no longer be able to boot on existing systems without the help of a rescue USB drive or similar.
    $ sudo PATH="$PATH" NIX_PATH="$NIX_PATH" `which nixos-install` --root /mnt

    Again, please refer to the nixos-install step in Chapter 2, Installing NixOS for more information.

    That should be it for installation to another partition!

  8. Optionally, you may want to clean up your non-NixOS distribution:

    $ sudo userdel nixbld
    $ sudo groupdel nixbld

    If you do not wish to keep the Nix package manager installed either, run something like sudo rm -rv ~/.nix-* /nix and remove the line that the Nix installer added to your ~/.profile.

  9. Note: The following steps are only for installing NixOS in place using NIXOS_LUSTRATE:

    Generate your NixOS configuration:

    $ sudo `which nixos-generate-config` --root /

    Note that this will place the generated configuration files in /etc/nixos. You'll probably want to edit the configuration files. Refer to the nixos-generate-config step in Chapter 2, Installing NixOS for more information.

    You'll likely want to set a root password for your first boot using the configuration files because you won't have a chance to enter a password until after you reboot. You can initalize the root password to an empty one with this line: (and of course don't forget to set one once you've rebooted or to lock the account with sudo passwd -l root if you use sudo)

    users.users.root.initialHashedPassword = "";
  10. Build the NixOS closure and install it in the system profile:

    $ nix-env -p /nix/var/nix/profiles/system -f '<nixpkgs/nixos>' -I nixos-config=/etc/nixos/configuration.nix -iA system
  11. Change ownership of the /nix tree to root (since your Nix install was probably single user):

    $ sudo chown -R 0.0 /nix
  12. Set up the /etc/NIXOS and /etc/NIXOS_LUSTRATE files:

    /etc/NIXOS officializes that this is now a NixOS partition (the bootup scripts require its presence).

    /etc/NIXOS_LUSTRATE tells the NixOS bootup scripts to move everything that's in the root partition to /old-root. This will move your existing distribution out of the way in the very early stages of the NixOS bootup. There are exceptions (we do need to keep NixOS there after all), so the NixOS lustrate process will not touch:

    • The /nix directory

    • The /boot directory

    • Any file or directory listed in /etc/NIXOS_LUSTRATE (one per line)


    Support for NIXOS_LUSTRATE was added in NixOS 16.09. The act of "lustrating" refers to the wiping of the existing distribution. Creating /etc/NIXOS_LUSTRATE can also be used on NixOS to remove all mutable files from your root partition (anything that's not in /nix or /boot gets "lustrated" on the next boot.

    lustrate /ˈlʌstreɪt/ verb.

    purify by expiatory sacrifice, ceremonial washing, or some other ritual action.

    Let's create the files:

    $ sudo touch /etc/NIXOS
    $ sudo touch /etc/NIXOS_LUSTRATE

    Let's also make sure the NixOS configuration files are kept once we reboot on NixOS:

    $ echo etc/nixos | sudo tee -a /etc/NIXOS_LUSTRATE
  13. Finally, move the /boot directory of your current distribution out of the way (the lustrate process will take care of the rest once you reboot, but this one must be moved out now because NixOS needs to install its own boot files:

    Warning: Once you complete this step, your current distribution will no longer be bootable! If you didn't get all the NixOS configuration right, especially those settings pertaining to boot loading and root partition, NixOS may not be bootable either. Have a USB rescue device ready in case this happens.
    $ sudo mv -v /boot /boot.bak &&
    sudo /nix/var/nix/profiles/system/bin/switch-to-configuration boot

    Cross your fingers, reboot, hopefully you should get a NixOS prompt!

  14. If for some reason you want to revert to the old distribution, you'll need to boot on a USB rescue disk and do something along these lines:

    # mkdir root
    # mount /dev/sdaX root
    # mkdir root/nixos-root
    # mv -v root/* root/nixos-root/
    # mv -v root/nixos-root/old-root/* root/
    # mv -v root/boot.bak root/boot  # We had renamed this by hand earlier
    # umount root
    # reboot

    This may work as is or you might also need to reinstall the boot loader

    And of course, if you're happy with NixOS and no longer need the old distribution:

    sudo rm -rf /old-root
  15. It's also worth noting that this whole process can be automated. This is especially useful for Cloud VMs, where provider do not provide NixOS. For instance, nixos-infect uses the lustrate process to convert Digital Ocean droplets to NixOS from other distributions automatically.

2.5.5. Installing behind a proxy

To install NixOS behind a proxy, do the following before running nixos-install.

  1. Update proxy configuration in /mnt/etc/nixos/configuration.nix to keep the internet accessible after reboot.

    networking.proxy.default = "http://user:password@proxy:port/";
    networking.proxy.noProxy = ",localhost,internal.domain";
  2. Setup the proxy environment variables in the shell where you are running nixos-install.

    # proxy_url="http://user:password@proxy:port/"
    # export http_proxy="$proxy_url"
    # export HTTP_PROXY="$proxy_url"
    # export https_proxy="$proxy_url"
    # export HTTPS_PROXY="$proxy_url"
Note: If you are switching networks with different proxy configurations, use the nesting.clone option in configuration.nix to switch proxies at runtime. Refer to Appendix A, Configuration Options for more information.

Chapter 3. Changing the Configuration

The file /etc/nixos/configuration.nix contains the current configuration of your machine. Whenever you’ve changed something in that file, you should do

# nixos-rebuild switch

to build the new configuration, make it the default configuration for booting, and try to realise the configuration in the running system (e.g., by restarting system services).

Warning: This command doesn't start/stop user services automatically. nixos-rebuild only runs a daemon-reload for each user with running user services.

Warning: These commands must be executed as root, so you should either run them from a root shell or by prefixing them with sudo -i.

You can also do

# nixos-rebuild test

to build the configuration and switch the running system to it, but without making it the boot default. So if (say) the configuration locks up your machine, you can just reboot to get back to a working configuration.

There is also

# nixos-rebuild boot

to build the configuration and make it the boot default, but not switch to it now (so it will only take effect after the next reboot).

You can make your configuration show up in a different submenu of the GRUB 2 boot screen by giving it a different profile name, e.g.

# nixos-rebuild switch -p test

which causes the new configuration (and previous ones created using -p test) to show up in the GRUB submenu “NixOS - Profile 'test'”. This can be useful to separate test configurations from “stable” configurations.

Finally, you can do

$ nixos-rebuild build

to build the configuration but nothing more. This is useful to see whether everything compiles cleanly.

If you have a machine that supports hardware virtualisation, you can also test the new configuration in a sandbox by building and running a QEMU virtual machine that contains the desired configuration. Just do

$ nixos-rebuild build-vm
$ ./result/bin/run-*-vm

The VM does not have any data from your host system, so your existing user accounts and home directories will not be available unless you have set mutableUsers = false. Another way is to temporarily add the following to your configuration:

users.users.your-user.initialHashedPassword = "test";

Important: delete the $hostname.qcow2 file if you have started the virtual machine at least once without the right users, otherwise the changes will not get picked up. You can forward ports on the host to the guest. For instance, the following will forward host port 2222 to guest port 22 (SSH):

$ QEMU_NET_OPTS="hostfwd=tcp::2222-:22" ./result/bin/run-*-vm

allowing you to log in via SSH (assuming you have set the appropriate passwords or SSH authorized keys):

$ ssh -p 2222 localhost

Chapter 4. Upgrading NixOS

Table of Contents

4.1. Automatic Upgrades

The best way to keep your NixOS installation up to date is to use one of the NixOS channels. A channel is a Nix mechanism for distributing Nix expressions and associated binaries. The NixOS channels are updated automatically from NixOS’s Git repository after certain tests have passed and all packages have been built. These channels are:

  • Stable channels, such as nixos-20.03. These only get conservative bug fixes and package upgrades. For instance, a channel update may cause the Linux kernel on your system to be upgraded from 4.19.34 to 4.19.38 (a minor bug fix), but not from 4.19.x to 4.20.x (a major change that has the potential to break things). Stable channels are generally maintained until the next stable branch is created.

  • The unstable channel, nixos-unstable. This corresponds to NixOS’s main development branch, and may thus see radical changes between channel updates. It’s not recommended for production systems.

  • Small channels, such as nixos-20.03-small or nixos-unstable-small. These are identical to the stable and unstable channels described above, except that they contain fewer binary packages. This means they get updated faster than the regular channels (for instance, when a critical security patch is committed to NixOS’s source tree), but may require more packages to be built from source than usual. They’re mostly intended for server environments and as such contain few GUI applications.

To see what channels are available, go to (Note that the URIs of the various channels redirect to a directory that contains the channel’s latest version and includes ISO images and VirtualBox appliances.) Please note that during the release process, channels that are not yet released will be present here as well. See the Getting NixOS page to find the newest supported stable release.

When you first install NixOS, you’re automatically subscribed to the NixOS channel that corresponds to your installation source. For instance, if you installed from a 20.03 ISO, you will be subscribed to the nixos-20.03 channel. To see which NixOS channel you’re subscribed to, run the following as root:

# nix-channel --list | grep nixos

To switch to a different NixOS channel, do

# nix-channel --add nixos

(Be sure to include the nixos parameter at the end.) For instance, to use the NixOS 20.03 stable channel:

# nix-channel --add nixos

If you have a server, you may want to use the “small” channel instead:

# nix-channel --add nixos

And if you want to live on the bleeding edge:

# nix-channel --add nixos

You can then upgrade NixOS to the latest version in your chosen channel by running

# nixos-rebuild switch --upgrade

which is equivalent to the more verbose nix-channel --update nixos; nixos-rebuild switch.

Note: Channels are set per user. This means that running nix-channel --add as a non root user (or without sudo) will not affect configuration in /etc/nixos/configuration.nix
Warning: It is generally safe to switch back and forth between channels. The only exception is that a newer NixOS may also have a newer Nix version, which may involve an upgrade of Nix’s database schema. This cannot be undone easily, so in that case you will not be able to go back to your original channel.

4.1. Automatic Upgrades

You can keep a NixOS system up-to-date automatically by adding the following to configuration.nix:

system.autoUpgrade.enable = true;
system.autoUpgrade.allowReboot = true;

This enables a periodically executed systemd service named nixos-upgrade.service. If the allowReboot option is false, it runs nixos-rebuild switch --upgrade to upgrade NixOS to the latest version in the current channel. (To see when the service runs, see systemctl list-timers.) If allowReboot is true, then the system will automatically reboot if the new generation contains a different kernel, initrd or kernel modules. You can also specify a channel explicitly, e.g. =;

Chapter 5. Configuration Syntax

The NixOS configuration file /etc/nixos/configuration.nix is actually a Nix expression, which is the Nix package manager’s purely functional language for describing how to build packages and configurations. This means you have all the expressive power of that language at your disposal, including the ability to abstract over common patterns, which is very useful when managing complex systems. The syntax and semantics of the Nix language are fully described in the Nix manual, but here we give a short overview of the most important constructs useful in NixOS configuration files.

5.1. NixOS Configuration File

The NixOS configuration file generally looks like this:

{ config, pkgs, ... }:

{ option definitions

The first line ({ config, pkgs, ... }:) denotes that this is actually a function that takes at least the two arguments config and pkgs. (These are explained later.) The function returns a set of option definitions ({ ... }). These definitions have the form name = value, where name is the name of an option and value is its value. For example,

{ config, pkgs, ... }:

{ services.httpd.enable = true;
  services.httpd.adminAddr = "";
  services.httpd.virtualHosts.localhost.documentRoot = "/webroot";

defines a configuration with three option definitions that together enable the Apache HTTP Server with /webroot as the document root.

Sets can be nested, and in fact dots in option names are shorthand for defining a set containing another set. For instance, services.httpd.enable defines a set named services that contains a set named httpd, which in turn contains an option definition named enable with value true. This means that the example above can also be written as:

{ config, pkgs, ... }:

{ services = {
    httpd = {
      enable = true;
      adminAddr = "";
      virtualHosts = {
        localhost = {
          documentRoot = "/webroot";

which may be more convenient if you have lots of option definitions that share the same prefix (such as services.httpd).

NixOS checks your option definitions for correctness. For instance, if you try to define an option that doesn’t exist (that is, doesn’t have a corresponding option declaration), nixos-rebuild will give an error like:

The option `services.httpd.enable' defined in `/etc/nixos/configuration.nix' does not exist.

Likewise, values in option definitions must have a correct type. For instance, services.httpd.enable must be a Boolean (true or false). Trying to give it a value of another type, such as a string, will cause an error:

The option value `services.httpd.enable' in `/etc/nixos/configuration.nix' is not a boolean.

Options have various types of values. The most important are:


Strings are enclosed in double quotes, e.g.

networking.hostName = "dexter";

Special characters can be escaped by prefixing them with a backslash (e.g. \").

Multi-line strings can be enclosed in double single quotes, e.g.

networking.extraHosts =
  '' other-localhost server

The main difference is that it strips from each line a number of spaces equal to the minimal indentation of the string as a whole (disregarding the indentation of empty lines), and that characters like " and \ are not special (making it more convenient for including things like shell code). See more info about this in the Nix manual here.


These can be true or false, e.g.

networking.firewall.enable = true;
networking.firewall.allowPing = false;


For example,

boot.kernel.sysctl."net.ipv4.tcp_keepalive_time" = 60;

(Note that here the attribute name net.ipv4.tcp_keepalive_time is enclosed in quotes to prevent it from being interpreted as a set named net containing a set named ipv4, and so on. This is because it’s not a NixOS option but the literal name of a Linux kernel setting.)


Sets were introduced above. They are name/value pairs enclosed in braces, as in the option definition

fileSystems."/boot" =
  { device = "/dev/sda1";
    fsType = "ext4";
    options = [ "rw" "data=ordered" "relatime" ];


The important thing to note about lists is that list elements are separated by whitespace, like this:

boot.kernelModules = [ "fuse" "kvm-intel" "coretemp" ];

List elements can be any other type, e.g. sets:

swapDevices = [ { device = "/dev/disk/by-label/swap"; } ];


Usually, the packages you need are already part of the Nix Packages collection, which is a set that can be accessed through the function argument pkgs. Typical uses:

environment.systemPackages =
  [ pkgs.thunderbird

services.postgresql.package = pkgs.postgresql_10;

The latter option definition changes the default PostgreSQL package used by NixOS’s PostgreSQL service to 10.x. For more information on packages, including how to add new ones, see Section 6.1.2, “Adding Custom Packages”.

5.2. Abstractions

If you find yourself repeating yourself over and over, it’s time to abstract. Take, for instance, this Apache HTTP Server configuration:

  services.httpd.virtualHosts =
    { "" = {
        documentRoot = "/webroot/";
        adminAddr = "";
        forceSSL = true;
        enableACME = true;
        enablePHP = true;
      "" = {
        documentRoot = "/webroot/";
        adminAddr = "";
        forceSSL = true;
        enableACME = true;
        enablePHP = true;

It defines two virtual hosts with nearly identical configuration; the only difference is the document root directories. To prevent this duplication, we can use a let:

  commonConfig =
    { adminAddr = "";
      forceSSL = true;
      enableACME = true;
  services.httpd.virtualHosts =
    { "" = (commonConfig // { documentRoot = "/webroot/"; });
      "" = (commonConfig // { documentRoot = "/webroot/"; });

The let commonConfig = ... defines a variable named commonConfig. The // operator merges two attribute sets, so the configuration of the second virtual host is the set commonConfig extended with the document root option.

You can write a let wherever an expression is allowed. Thus, you also could have written:

  services.httpd.virtualHosts =
    let commonConfig = ...; in
    { "" = (commonConfig // { ... })
      "" = (commonConfig // { ... })

but not { let commonConfig = ...; in ...; } since attributes (as opposed to attribute values) are not expressions.

Functions provide another method of abstraction. For instance, suppose that we want to generate lots of different virtual hosts, all with identical configuration except for the document root. This can be done as follows:

  services.httpd.virtualHosts =
      makeVirtualHost = webroot:
        { documentRoot = webroot;
          adminAddr = "";
          forceSSL = true;
          enableACME = true;
      { "" = (makeVirtualHost "/webroot/");
        "" = (makeVirtualHost "/webroot/");
        "" = (makeVirtualHost "/webroot/");
        "" = (makeVirtualHost "/webroot/");

Here, makeVirtualHost is a function that takes a single argument webroot and returns the configuration for a virtual host. That function is then called for several names to produce the list of virtual host configurations.

5.3. Modularity

The NixOS configuration mechanism is modular. If your configuration.nix becomes too big, you can split it into multiple files. Likewise, if you have multiple NixOS configurations (e.g. for different computers) with some commonality, you can move the common configuration into a shared file.

Modules have exactly the same syntax as configuration.nix. In fact, configuration.nix is itself a module. You can use other modules by including them from configuration.nix, e.g.:

{ config, pkgs, ... }:

{ imports = [ ./vpn.nix ./kde.nix ];
  services.httpd.enable = true;
  environment.systemPackages = [ pkgs.emacs ];

Here, we include two modules from the same directory, vpn.nix and kde.nix. The latter might look like this:

{ config, pkgs, ... }:

{ services.xserver.enable = true;
  services.xserver.displayManager.sddm.enable = true;
  services.xserver.desktopManager.plasma5.enable = true;

Note that both configuration.nix and kde.nix define the option environment.systemPackages. When multiple modules define an option, NixOS will try to merge the definitions. In the case of environment.systemPackages, that’s easy: the lists of packages can simply be concatenated. The value in configuration.nix is merged last, so for list-type options, it will appear at the end of the merged list. If you want it to appear first, you can use mkBefore:

boot.kernelModules = mkBefore [ "kvm-intel" ];

This causes the kvm-intel kernel module to be loaded before any other kernel modules.

For other types of options, a merge may not be possible. For instance, if two modules define services.httpd.adminAddr, nixos-rebuild will give an error:

The unique option `services.httpd.adminAddr' is defined multiple times, in `/etc/nixos/httpd.nix' and `/etc/nixos/configuration.nix'.

When that happens, it’s possible to force one definition take precedence over the others:

services.httpd.adminAddr = pkgs.lib.mkForce "";

When using multiple modules, you may need to access configuration values defined in other modules. This is what the config function argument is for: it contains the complete, merged system configuration. That is, config is the result of combining the configurations returned by every module [1] . For example, here is a module that adds some packages to environment.systemPackages only if services.xserver.enable is set to true somewhere else:

{ config, pkgs, ... }:

{ environment.systemPackages =
    if then
      [ pkgs.firefox
      [ ];

With multiple modules, it may not be obvious what the final value of a configuration option is. The command nixos-option allows you to find out:

$ nixos-option services.xserver.enable

$ nixos-option boot.kernelModules
[ "tun" "ipv6" "loop" ... ]

Interactive exploration of the configuration is possible using nix repl, a read-eval-print loop for Nix expressions. A typical use:

$ nix repl '<nixpkgs/nixos>'

nix-repl> config.networking.hostName

nix-repl> map (x: x.hostName)
[ "" "" ]

While abstracting your configuration, you may find it useful to generate modules using code, instead of writing files. The example below would have the same effect as importing a file which sets those options.

{ config, pkgs, ... }:

let netConfig = { hostName }: {
  networking.hostName = hostName;
  networking.useDHCP = false;


{ imports = [ (netConfig "nixos.localdomain") ]; }

5.4. Syntax Summary

Below is a summary of the most important syntactic constructs in the Nix expression language. It’s not complete. In particular, there are many other built-in functions. See the Nix manual for the rest.

Basic values
"Hello world" A string
"${pkgs.bash}/bin/sh" A string containing an expression (expands to "/nix/store/hash-bash-version/bin/sh")
true, false Booleans
123 An integer
./foo.png A path (relative to the containing Nix expression)
Compound values
{ x = 1; y = 2; } A set with attributes named x and y
{ = 1; } A nested set, equivalent to { foo = { bar = 1; }; }
rec { x = "foo"; y = x + "bar"; } A recursive set, equivalent to { x = "foo"; y = "foobar"; }
[ "foo" "bar" ] A list with two elements
"foo" + "bar" String concatenation
1 + 2 Integer addition
"foo" == "f" + "oo" Equality test (evaluates to true)
"foo" != "bar" Inequality test (evaluates to true)
!true Boolean negation
{ x = 1; y = 2; }.x Attribute selection (evaluates to 1)
{ x = 1; y = 2; }.z or 3 Attribute selection with default (evaluates to 3)
{ x = 1; y = 2; } // { z = 3; } Merge two sets (attributes in the right-hand set taking precedence)
Control structures
if 1 + 1 == 2 then "yes!" else "no!" Conditional expression
assert 1 + 1 == 2; "yes!" Assertion check (evaluates to "yes!"). See Section 44.4, “Warnings and Assertions” for using assertions in modules
let x = "foo"; y = "bar"; in x + y Variable definition
with pkgs.lib; head [ 1 2 3 ] Add all attributes from the given set to the scope (evaluates to 1)
Functions (lambdas)
x: x + 1 A function that expects an integer and returns it increased by 1
(x: x + 1) 100 A function call (evaluates to 101)
let inc = x: x + 1; in inc (inc (inc 100)) A function bound to a variable and subsequently called by name (evaluates to 103)
{ x, y }: x + y A function that expects a set with required attributes x and y and concatenates them
{ x, y ? "bar" }: x + y A function that expects a set with required attribute x and optional y, using "bar" as default value for y
{ x, y, ... }: x + y A function that expects a set with required attributes x and y and ignores any other attributes
{ x, y } @ args: x + y A function that expects a set with required attributes x and y, and binds the whole set to args
Built-in functions
import ./foo.nix Load and return Nix expression in given file
map (x: x + x) [ 1 2 3 ] Apply a function to every element of a list (evaluates to [ 2 4 6 ])

[1] If you’re wondering how it’s possible that the (indirect) result of a function is passed as an input to that same function: that’s because Nix is a “lazy” language — it only computes values when they are needed. This works as long as no individual configuration value depends on itself.

Chapter 6. Package Management

This section describes how to add additional packages to your system. NixOS has two distinct styles of package management:

  • Declarative, where you declare what packages you want in your configuration.nix. Every time you run nixos-rebuild, NixOS will ensure that you get a consistent set of binaries corresponding to your specification.

  • Ad hoc, where you install, upgrade and uninstall packages via the nix-env command. This style allows mixing packages from different Nixpkgs versions. It’s the only choice for non-root users.

6.1. Declarative Package Management

With declarative package management, you specify which packages you want on your system by setting the option environment.systemPackages. For instance, adding the following line to configuration.nix enables the Mozilla Thunderbird email application:

environment.systemPackages = [ pkgs.thunderbird ];

The effect of this specification is that the Thunderbird package from Nixpkgs will be built or downloaded as part of the system when you run nixos-rebuild switch.

Note: Some packages require additional global configuration such as D-Bus or systemd service registration so adding them to environment.systemPackages might not be sufficient. You are advised to check the list of options whether a NixOS module for the package does not exist.

You can get a list of the available packages as follows:

$ nix-env -qaP '*' --description
nixos.firefox   firefox-23.0   Mozilla Firefox - the browser, reloaded

The first column in the output is the attribute name, such as nixos.thunderbird.

Note: the nixos prefix tells us that we want to get the package from the nixos channel and works only in CLI tools. In declarative configuration use pkgs prefix (variable).

To “uninstall” a package, simply remove it from environment.systemPackages and run nixos-rebuild switch.

6.1.1. Customising Packages

Some packages in Nixpkgs have options to enable or disable optional functionality or change other aspects of the package. For instance, the Firefox wrapper package (which provides Firefox with a set of plugins such as the Adobe Flash player) has an option to enable the Google Talk plugin. It can be set in configuration.nix as follows: nixpkgs.config.firefox.enableGoogleTalkPlugin = true;

Warning: Unfortunately, Nixpkgs currently lacks a way to query available configuration options.

Apart from high-level options, it’s possible to tweak a package in almost arbitrary ways, such as changing or disabling dependencies of a package. For instance, the Emacs package in Nixpkgs by default has a dependency on GTK 2. If you want to build it against GTK 3, you can specify that as follows:

environment.systemPackages = [ (pkgs.emacs.override { gtk = pkgs.gtk3; }) ];

The function override performs the call to the Nix function that produces Emacs, with the original arguments amended by the set of arguments specified by you. So here the function argument gtk gets the value pkgs.gtk3, causing Emacs to depend on GTK 3. (The parentheses are necessary because in Nix, function application binds more weakly than list construction, so without them, environment.systemPackages would be a list with two elements.)

Even greater customisation is possible using the function overrideAttrs. While the override mechanism above overrides the arguments of a package function, overrideAttrs allows changing the attributes passed to mkDerivation. This permits changing any aspect of the package, such as the source code. For instance, if you want to override the source code of Emacs, you can say:

environment.systemPackages = [
  (pkgs.emacs.overrideAttrs (oldAttrs: {
    name = "emacs-25.0-pre";
    src = /path/to/my/emacs/tree;

Here, overrideAttrs takes the Nix derivation specified by pkgs.emacs and produces a new derivation in which the original’s name and src attribute have been replaced by the given values by re-calling stdenv.mkDerivation. The original attributes are accessible via the function argument, which is conventionally named oldAttrs.

The overrides shown above are not global. They do not affect the original package; other packages in Nixpkgs continue to depend on the original rather than the customised package. This means that if another package in your system depends on the original package, you end up with two instances of the package. If you want to have everything depend on your customised instance, you can apply a global override as follows:

nixpkgs.config.packageOverrides = pkgs:
  { emacs = pkgs.emacs.override { gtk = pkgs.gtk3; };

The effect of this definition is essentially equivalent to modifying the emacs attribute in the Nixpkgs source tree. Any package in Nixpkgs that depends on emacs will be passed your customised instance. (However, the value pkgs.emacs in nixpkgs.config.packageOverrides refers to the original rather than overridden instance, to prevent an infinite recursion.)

6.1.2. Adding Custom Packages

It’s possible that a package you need is not available in NixOS. In that case, you can do two things. First, you can clone the Nixpkgs repository, add the package to your clone, and (optionally) submit a patch or pull request to have it accepted into the main Nixpkgs repository. This is described in detail in the Nixpkgs manual. In short, you clone Nixpkgs:

$ git clone
$ cd nixpkgs

Then you write and test the package as described in the Nixpkgs manual. Finally, you add it to environment.systemPackages, e.g.

environment.systemPackages = [ ];

and you run nixos-rebuild, specifying your own Nixpkgs tree:

# nixos-rebuild switch -I nixpkgs=/path/to/my/nixpkgs

The second possibility is to add the package outside of the Nixpkgs tree. For instance, here is how you specify a build of the GNU Hello package directly in configuration.nix:

environment.systemPackages =
    my-hello = with pkgs; stdenv.mkDerivation rec {
      name = "hello-2.8";
      src = fetchurl {
        url = "mirror://gnu/hello/${name}.tar.gz";
        sha256 = "0wqd8sjmxfskrflaxywc7gqw7sfawrfvdxd9skxawzfgyy0pzdz6";
  [ my-hello ];

Of course, you can also move the definition of my-hello into a separate Nix expression, e.g.

environment.systemPackages = [ (import ./my-hello.nix) ];

where my-hello.nix contains:

with import <nixpkgs> {}; # bring all of Nixpkgs into scope

stdenv.mkDerivation rec {
  name = "hello-2.8";
  src = fetchurl {
    url = "mirror://gnu/hello/${name}.tar.gz";
    sha256 = "0wqd8sjmxfskrflaxywc7gqw7sfawrfvdxd9skxawzfgyy0pzdz6";

This allows testing the package easily:

$ nix-build my-hello.nix
$ ./result/bin/hello
Hello, world!

6.2. Ad-Hoc Package Management

With the command nix-env, you can install and uninstall packages from the command line. For instance, to install Mozilla Thunderbird:

$ nix-env -iA nixos.thunderbird

If you invoke this as root, the package is installed in the Nix profile /nix/var/nix/profiles/default and visible to all users of the system; otherwise, the package ends up in /nix/var/nix/profiles/per-user/username/profile and is not visible to other users. The -A flag specifies the package by its attribute name; without it, the package is installed by matching against its package name (e.g. thunderbird). The latter is slower because it requires matching against all available Nix packages, and is ambiguous if there are multiple matching packages.

Packages come from the NixOS channel. You typically upgrade a package by updating to the latest version of the NixOS channel:

$ nix-channel --update nixos

and then running nix-env -i again. Other packages in the profile are not affected; this is the crucial difference with the declarative style of package management, where running nixos-rebuild switch causes all packages to be updated to their current versions in the NixOS channel. You can however upgrade all packages for which there is a newer version by doing:

$ nix-env -u '*'

A package can be uninstalled using the -e flag:

$ nix-env -e thunderbird

Finally, you can roll back an undesirable nix-env action:

$ nix-env --rollback

nix-env has many more flags. For details, see the nix-env(1) manpage or the Nix manual.

Chapter 7. User Management

NixOS supports both declarative and imperative styles of user management. In the declarative style, users are specified in configuration.nix. For instance, the following states that a user account named alice shall exist:

users.users.alice = {
  isNormalUser = true;
  home = "/home/alice";
  description = "Alice Foobar";
  extraGroups = [ "wheel" "networkmanager" ];
  openssh.authorizedKeys.keys = [ "ssh-dss AAAAB3Nza... alice@foobar" ];

Note that alice is a member of the wheel and networkmanager groups, which allows her to use sudo to execute commands as root and to configure the network, respectively. Also note the SSH public key that allows remote logins with the corresponding private key. Users created in this way do not have a password by default, so they cannot log in via mechanisms that require a password. However, you can use the passwd program to set a password, which is retained across invocations of nixos-rebuild.

If you set users.mutableUsers to false, then the contents of /etc/passwd and /etc/group will be congruent to your NixOS configuration. For instance, if you remove a user from users.users and run nixos-rebuild, the user account will cease to exist. Also, imperative commands for managing users and groups, such as useradd, are no longer available. Passwords may still be assigned by setting the user's hashedPassword option. A hashed password can be generated using mkpasswd -m sha-512 after installing the mkpasswd package.

A user ID (uid) is assigned automatically. You can also specify a uid manually by adding

uid = 1000;

to the user specification.

Groups can be specified similarly. The following states that a group named students shall exist:

users.groups.students.gid = 1000;

As with users, the group ID (gid) is optional and will be assigned automatically if it’s missing.

In the imperative style, users and groups are managed by commands such as useradd, groupmod and so on. For instance, to create a user account named alice:

# useradd -m alice

To make all nix tools available to this new user use `su - USER` which opens a login shell (==shell that loads the profile) for given user. This will create the ~/.nix-defexpr symlink. So run:

# su - alice -c "true"

The flag -m causes the creation of a home directory for the new user, which is generally what you want. The user does not have an initial password and therefore cannot log in. A password can be set using the passwd utility:

# passwd alice
Enter new UNIX password: ***
Retype new UNIX password: ***

A user can be deleted using userdel:

# userdel -r alice

The flag -r deletes the user’s home directory. Accounts can be modified using usermod. Unix groups can be managed using groupadd, groupmod and groupdel.

Chapter 8. File Systems

You can define file systems using the fileSystems configuration option. For instance, the following definition causes NixOS to mount the Ext4 file system on device /dev/disk/by-label/data onto the mount point /data:

fileSystems."/data" =
  { device = "/dev/disk/by-label/data";
    fsType = "ext4";

Mount points are created automatically if they don’t already exist. For device, it’s best to use the topology-independent device aliases in /dev/disk/by-label and /dev/disk/by-uuid, as these don’t change if the topology changes (e.g. if a disk is moved to another IDE controller).

You can usually omit the file system type (fsType), since mount can usually detect the type and load the necessary kernel module automatically. However, if the file system is needed at early boot (in the initial ramdisk) and is not ext2, ext3 or ext4, then it’s best to specify fsType to ensure that the kernel module is available.

Note: System startup will fail if any of the filesystems fails to mount, dropping you to the emergency shell. You can make a mount asynchronous and non-critical by adding options = [ "nofail" ];.

8.1. LUKS-Encrypted File Systems

NixOS supports file systems that are encrypted using LUKS (Linux Unified Key Setup). For example, here is how you create an encrypted Ext4 file system on the device /dev/disk/by-uuid/3f6b0024-3a44-4fde-a43a-767b872abe5d:

# cryptsetup luksFormat /dev/disk/by-uuid/3f6b0024-3a44-4fde-a43a-767b872abe5d

This will overwrite data on /dev/disk/by-uuid/3f6b0024-3a44-4fde-a43a-767b872abe5d irrevocably.

Are you sure? (Type uppercase yes): YES
Enter LUKS passphrase: ***
Verify passphrase: ***

# cryptsetup luksOpen /dev/disk/by-uuid/3f6b0024-3a44-4fde-a43a-767b872abe5d crypted
Enter passphrase for /dev/disk/by-uuid/3f6b0024-3a44-4fde-a43a-767b872abe5d: ***

# mkfs.ext4 /dev/mapper/crypted

To ensure that this file system is automatically mounted at boot time as /, add the following to configuration.nix:

boot.initrd.luks.devices.crypted.device = "/dev/disk/by-uuid/3f6b0024-3a44-4fde-a43a-767b872abe5d";
fileSystems."/".device = "/dev/mapper/crypted";

Should grub be used as bootloader, and /boot is located on an encrypted partition, it is necessary to add the following grub option:

boot.loader.grub.enableCryptodisk = true;

8.1.1. FIDO2

NixOS also supports unlocking your LUKS-Encrypted file system using a FIDO2 compatible token. In the following example, we will create a new FIDO2 credential and add it as a new key to our existing device /dev/sda2:

# export FIDO2_LABEL="/dev/sda2 @ $HOSTNAME"
# fido2luks credential "$FIDO2_LABEL"

# fido2luks -i add-key /dev/sda2 f1d00200108b9d6e849a8b388da457688e3dd653b4e53770012d8f28e5d3b269865038c346802f36f3da7278b13ad6a3bb6a1452e24ebeeaa24ba40eef559b1b287d2a2f80b7
Password (again):
Old password:
Old password (again):
Added to key to device /dev/sda2, slot: 2

To ensure that this file system is decrypted using the FIDO2 compatible key, add the following to configuration.nix:

boot.initrd.luks.fido2Support = true;
boot.initrd.luks.devices."/dev/sda2".fido2.credential = "f1d00200108b9d6e849a8b388da457688e3dd653b4e53770012d8f28e5d3b269865038c346802f36f3da7278b13ad6a3bb6a1452e24ebeeaa24ba40eef559b1b287d2a2f80b7";

You can also use the FIDO2 passwordless setup, but for security reasons, you might want to enable it only when your device is PIN protected, such as Trezor.

boot.initrd.luks.devices."/dev/sda2".fido2.passwordLess = true;

Chapter 9. X Window System

The X Window System (X11) provides the basis of NixOS’ graphical user interface. It can be enabled as follows:

services.xserver.enable = true;

The X server will automatically detect and use the appropriate video driver from a set of drivers (such as vesa and intel). You can also specify a driver manually, e.g.

services.xserver.videoDrivers = [ "r128" ];

to enable’s xf86-video-r128 driver.

You also need to enable at least one desktop or window manager. Otherwise, you can only log into a plain undecorated xterm window. Thus you should pick one or more of the following lines:

services.xserver.desktopManager.plasma5.enable = true;
services.xserver.desktopManager.xfce.enable = true;
services.xserver.desktopManager.gnome3.enable = true;
services.xserver.desktopManager.mate.enable = true;
services.xserver.windowManager.xmonad.enable = true;
services.xserver.windowManager.twm.enable = true;
services.xserver.windowManager.icewm.enable = true;
services.xserver.windowManager.i3.enable = true;

NixOS’s default display manager (the program that provides a graphical login prompt and manages the X server) is LightDM. You can select an alternative one by picking one of the following lines:

services.xserver.displayManager.sddm.enable = true;
services.xserver.displayManager.gdm.enable = true;

You can set the keyboard layout (and optionally the layout variant):

services.xserver.layout = "de";
services.xserver.xkbVariant = "neo";

The X server is started automatically at boot time. If you don’t want this to happen, you can set:

services.xserver.autorun = false;

The X server can then be started manually:

# systemctl start display-manager.service

On 64-bit systems, if you want OpenGL for 32-bit programs such as in Wine, you should also set the following:

hardware.opengl.driSupport32Bit = true;


The x11 login screen can be skipped entirely, automatically logging you into your window manager and desktop environment when you boot your computer.

This is especially helpful if you have disk encryption enabled. Since you already have to provide a password to decrypt your disk, entering a second password to login can be redundant.

To enable auto-login, you need to define your default window manager and desktop environment. If you wanted no desktop environment and i3 as your your window manager, you'd define:

services.xserver.displayManager.defaultSession = "none+i3";

Every display manager in NixOS supports auto-login, here is an example using lightdm for a user alice:

services.xserver.displayManager.lightdm.enable = true;
services.xserver.displayManager.lightdm.autoLogin.enable = true;
services.xserver.displayManager.lightdm.autoLogin.user = "alice";

The options are named identically for all other display managers.

Proprietary NVIDIA drivers

NVIDIA provides a proprietary driver for its graphics cards that has better 3D performance than the drivers. It is not enabled by default because it’s not free software. You can enable it as follows:

services.xserver.videoDrivers = [ "nvidia" ];

Or if you have an older card, you may have to use one of the legacy drivers:

services.xserver.videoDrivers = [ "nvidiaLegacy390" ];
services.xserver.videoDrivers = [ "nvidiaLegacy340" ];
services.xserver.videoDrivers = [ "nvidiaLegacy304" ];
services.xserver.videoDrivers = [ "nvidiaLegacy173" ];

You may need to reboot after enabling this driver to prevent a clash with other kernel modules.

Proprietary AMD drivers

AMD provides a proprietary driver for its graphics cards that has better 3D performance than the drivers. It is not enabled by default because it’s not free software. You can enable it as follows:

services.xserver.videoDrivers = [ "ati_unfree" ];

You will need to reboot after enabling this driver to prevent a clash with other kernel modules.

Note: For recent AMD GPUs you most likely want to keep either the defaults or "amdgpu" (both free).


Support for Synaptics touchpads (found in many laptops such as the Dell Latitude series) can be enabled as follows:

services.xserver.libinput.enable = true;

The driver has many options (see Appendix A, Configuration Options). For instance, the following disables tap-to-click behavior:

services.xserver.libinput.tapping = false;

Note: the use of services.xserver.synaptics is deprecated since NixOS 17.09.

GTK/Qt themes

GTK themes can be installed either to user profile or system-wide (via environment.systemPackages). To make Qt 5 applications look similar to GTK2 ones, you can install qt5.qtbase.gtk package into your system environment. It should work for all Qt 5 library versions.

Custom XKB layouts

It is possible to install custom XKB keyboard layouts using the option services.xserver.extraLayouts . As a first example, we are going to create a layout based on the basic US layout, with an additional layer to type some greek symbols by pressing the right-alt key.

To do this we are going to create a us-greek file with a xkb_symbols section.

xkb_symbols "us-greek"
  include "us(basic)"            // includes the base US keys
  include "level3(ralt_switch)"  // configures right alt as a third level switch

  key <LatA> { [ a, A, Greek_alpha ] };
  key <LatB> { [ b, B, Greek_beta  ] };
  key <LatG> { [ g, G, Greek_gamma ] };
  key <LatD> { [ d, D, Greek_delta ] };
  key <LatZ> { [ z, Z, Greek_zeta  ] };

To install the layout, the filepath, a description and the list of languages must be given: = {
  description = "US layout with alt-gr greek";
  languages   = [ "eng" ];
  symbolsFile = /path/to/us-greek;
Note: The name should match the one given to the xkb_symbols block.

The layout should now be installed and ready to use: try it by running setxkbmap us-greek and type <alt>+a. To change the default the usual services.xserver.layout option can still be used.

A layout can have several other components besides xkb_symbols, for example we will define new keycodes for some multimedia key and bind these to some symbol.

Use the xev utility from pkgs.xorg.xev to find the codes of the keys of interest, then create a media-key file to hold the keycodes definitions

xkb_keycodes "media"
 <volUp>   = 123;
 <volDown> = 456;

Now use the newly define keycodes in media-sym:

xkb_symbols "media"
 key.type = "ONE_LEVEL";
 key <volUp>   { [ XF86AudioLowerVolume ] };
 key <volDown> { [ XF86AudioRaiseVolume ] };

As before, to install the layout do = {
  description  = "Multimedia keys remapping";
  languages    = [ "eng" ];
  symbolsFile  = /path/to/media-key;
  keycodesFile = /path/to/media-sym;
Note: The function pkgs.writeText <filename> <content> can be useful if you prefer to keep the layout definitions inside the NixOS configuration.

Unfortunately, the Xorg server does not (currently) support setting a keymap directly but relies instead on XKB rules to select the matching components (keycodes, types, ...) of a layout. This means that components other than symbols won't be loaded by default. As a workaround, you can set the keymap using setxkbmap at the start of the session with:

services.xserver.displayManager.sessionCommands = "setxkbmap -keycodes media";

If you are manually starting the X server, you should set the argument -xkbdir /etc/X11/xkb, otherwise X won't find your layout files. For example with xinit run

$ xinit -- -xkbdir /etc/X11/xkb

To learn how to write layouts take a look at the XKB documentation . More example layouts can also be found here .

Chapter 10. Xfce Desktop Environment

To enable the Xfce Desktop Environment, set

services.xserver.desktopManager.xfce.enable = true;
services.xserver.displayManager.defaultSession = "xfce";

Optionally, picom can be enabled for nice graphical effects, some example settings:

services.picom = {
  enable          = true;
  fade            = true;
  inactiveOpacity = "0.9";
  shadow          = true;
  fadeDelta       = 4;

Some Xfce programs are not installed automatically. To install them manually (system wide), put them into your environment.systemPackages from pkgs.xfce.

Thunar Plugins

If you'd like to add extra plugins to Thunar, add them to services.xserver.desktopManager.xfce.thunarPlugins. You shouldn't just add them to environment.systemPackages.


Even after enabling udisks2, volume management might not work. Thunar and/or the desktop takes time to show up. Thunar will spit out this kind of message on start (look at journalctl --user -b).

Thunar:2410): GVFS-RemoteVolumeMonitor-WARNING **: remote volume monitor with dbus name org.gtk.Private.UDisks2VolumeMonitor is not supported

This is caused by some needed GNOME services not running. This is all fixed by enabling "Launch GNOME services on startup" in the Advanced tab of the Session and Startup settings panel. Alternatively, you can run this command to do the same thing.

$ xfconf-query -c xfce4-session -p /compat/LaunchGNOME -s true

A log-out and re-log will be needed for this to take effect.

Chapter 11. Networking

This section describes how to configure networking components on your NixOS machine.

11.1. NetworkManager

To facilitate network configuration, some desktop environments use NetworkManager. You can enable NetworkManager by setting:

networking.networkmanager.enable = true;

some desktop managers (e.g., GNOME) enable NetworkManager automatically for you.

All users that should have permission to change network settings must belong to the networkmanager group:

users.users.alice.extraGroups = [ "networkmanager" ];

NetworkManager is controlled using either nmcli or nmtui (curses-based terminal user interface). See their manual pages for details on their usage. Some desktop environments (GNOME, KDE) have their own configuration tools for NetworkManager. On XFCE, there is no configuration tool for NetworkManager by default: by enabling programs.nm-applet.enable, the graphical applet will be installed and will launch automatically when the graphical session is started.


networking.networkmanager and networking.wireless (WPA Supplicant) can be used together if desired. To do this you need to instruct NetworkManager to ignore those interfaces like:

networking.networkmanager.unmanaged = [
   "*" "except:type:wwan" "except:type:gsm"

Refer to the option description for the exact syntax and references to external documentation.

11.2. Secure Shell Access

Secure shell (SSH) access to your machine can be enabled by setting:

services.openssh.enable = true;

By default, root logins using a password are disallowed. They can be disabled entirely by setting services.openssh.permitRootLogin to "no".

You can declaratively specify authorised RSA/DSA public keys for a user as follows:

users.users.alice.openssh.authorizedKeys.keys =
  [ "ssh-dss AAAAB3NzaC1kc3MAAACBAPIkGWVEt4..." ];

11.3. IPv4 Configuration

By default, NixOS uses DHCP (specifically, dhcpcd) to automatically configure network interfaces. However, you can configure an interface manually as follows:

networking.interfaces.eth0.ipv4.addresses = [ {
  address = "";
  prefixLength = 24;
} ];

Typically you’ll also want to set a default gateway and set of name servers:

networking.defaultGateway = "";
networking.nameservers = [ "" ];

Note: Statically configured interfaces are set up by the systemd service interface-name-cfg.service. The default gateway and name server configuration is performed by network-setup.service.

The host name is set using networking.hostName:

networking.hostName = "cartman";

The default host name is nixos. Set it to the empty string ("") to allow the DHCP server to provide the host name.

11.4. IPv6 Configuration

IPv6 is enabled by default. Stateless address autoconfiguration is used to automatically assign IPv6 addresses to all interfaces. You can disable IPv6 support globally by setting:

networking.enableIPv6 = false;

You can disable IPv6 on a single interface using a normal sysctl (in this example, we use interface eth0):

boot.kernel.sysctl."net.ipv6.conf.eth0.disable_ipv6" = true;

As with IPv4 networking interfaces are automatically configured via DHCPv6. You can configure an interface manually:

networking.interfaces.eth0.ipv6.addresses = [ {
  address = "fe00:aa:bb:cc::2";
  prefixLength = 64;
} ];

For configuring a gateway, optionally with explicitly specified interface:

networking.defaultGateway6 = {
  address = "fe00::1";
  interface = "enp0s3";

See Section 11.3, “IPv4 Configuration” for similar examples and additional information.

11.5. Firewall

NixOS has a simple stateful firewall that blocks incoming connections and other unexpected packets. The firewall applies to both IPv4 and IPv6 traffic. It is enabled by default. It can be disabled as follows:

networking.firewall.enable = false;

If the firewall is enabled, you can open specific TCP ports to the outside world:

networking.firewall.allowedTCPPorts = [ 80 443 ];

Note that TCP port 22 (ssh) is opened automatically if the SSH daemon is enabled (services.openssh.enable = true). UDP ports can be opened through networking.firewall.allowedUDPPorts.

To open ranges of TCP ports:

networking.firewall.allowedTCPPortRanges = [
  { from = 4000; to = 4007; }
  { from = 8000; to = 8010; }

Similarly, UDP port ranges can be opened through networking.firewall.allowedUDPPortRanges.

11.6. Wireless Networks

For a desktop installation using NetworkManager (e.g., GNOME), you just have to make sure the user is in the networkmanager group and you can skip the rest of this section on wireless networks.

NixOS will start wpa_supplicant for you if you enable this setting:

networking.wireless.enable = true;

NixOS lets you specify networks for wpa_supplicant declaratively:

networking.wireless.networks = {
  echelon = {                # SSID with no spaces or special characters
    psk = "abcdefgh";
  "echelon's AP" = {         # SSID with spaces and/or special characters
    psk = "ijklmnop";
  echelon = {                # Hidden SSID
    hidden = true;
    psk = "qrstuvwx";
  free.wifi = {};            # Public wireless network

Be aware that keys will be written to the nix store in plaintext! When no networks are set, it will default to using a configuration file at /etc/wpa_supplicant.conf. You should edit this file yourself to define wireless networks, WPA keys and so on (see wpa_supplicant.conf(5)).

If you are using WPA2 you can generate pskRaw key using wpa_passphrase:

$ wpa_passphrase ESSID PSK

networking.wireless.networks = {
  echelon = {
    pskRaw = "dca6d6ed41f4ab5a984c9f55f6f66d4efdc720ebf66959810f4329bb391c5435";

or you can use it to directly generate the wpa_supplicant.conf:

# wpa_passphrase ESSID PSK > /etc/wpa_supplicant.conf

After you have edited the wpa_supplicant.conf, you need to restart the wpa_supplicant service.

# systemctl restart wpa_supplicant.service

11.7. Ad-Hoc Configuration

You can use networking.localCommands to specify shell commands to be run at the end of network-setup.service. This is useful for doing network configuration not covered by the existing NixOS modules. For instance, to statically configure an IPv6 address:

networking.localCommands =
    ip -6 addr add 2001:610:685:1::1/64 dev eth0

Chapter 12. Linux Kernel

You can override the Linux kernel and associated packages using the option boot.kernelPackages. For instance, this selects the Linux 3.10 kernel:

boot.kernelPackages = pkgs.linuxPackages_3_10;

Note that this not only replaces the kernel, but also packages that are specific to the kernel version, such as the NVIDIA video drivers. This ensures that driver packages are consistent with the kernel.

The default Linux kernel configuration should be fine for most users. You can see the configuration of your current kernel with the following command:

zcat /proc/config.gz

If you want to change the kernel configuration, you can use the packageOverrides feature (see Section 6.1.1, “Customising Packages”). For instance, to enable support for the kernel debugger KGDB:

nixpkgs.config.packageOverrides = pkgs:
  { linux_3_4 = pkgs.linux_3_4.override {
      extraConfig =
          KGDB y

extraConfig takes a list of Linux kernel configuration options, one per line. The name of the option should not include the prefix CONFIG_. The option value is typically y, n or m (to build something as a kernel module).

Kernel modules for hardware devices are generally loaded automatically by udev. You can force a module to be loaded via boot.kernelModules, e.g.

boot.kernelModules = [ "fuse" "kvm-intel" "coretemp" ];

If the module is required early during the boot (e.g. to mount the root file system), you can use boot.initrd.kernelModules:

boot.initrd.kernelModules = [ "cifs" ];

This causes the specified modules and their dependencies to be added to the initial ramdisk.

Kernel runtime parameters can be set through boot.kernel.sysctl, e.g.

boot.kernel.sysctl."net.ipv4.tcp_keepalive_time" = 120;

sets the kernel’s TCP keepalive time to 120 seconds. To see the available parameters, run sysctl -a.

12.1. Customize your kernel

The first step before compiling the kernel is to generate an appropriate .config configuration. Either you pass your own config via the configfile setting of linuxManualConfig:

  custom-kernel = super.linuxManualConfig {
    inherit (super) stdenv hostPlatform;
    inherit (linux_4_9) src;
    version = "${linux_4_9.version}-custom";

    configfile = /home/me/my_kernel_config;
    allowImportFromDerivation = true;

You can edit the config with this snippet (by default make menuconfig won't work out of the box on nixos):

      nix-shell -E 'with import <nixpkgs> {}; kernelToOverride.overrideAttrs (o: {nativeBuildInputs=o.nativeBuildInputs ++ [ pkgconfig ncurses ];})'

or you can let nixpkgs generate the configuration. Nixpkgs generates it via answering the interactive kernel utility make config. The answers depend on parameters passed to pkgs/os-specific/linux/kernel/generic.nix (which you can influence by overriding extraConfig, autoModules, modDirVersion, preferBuiltin, extraConfig).

  mptcp93.override ({

      ignoreConfigErrors = true;
      autoModules = false;
      kernelPreferBuiltin = true;

      enableParallelBuilding = true;

      extraConfig = ''
        DEBUG_KERNEL y
        KGDB y
        DEBUG_INFO y

12.2. Developing kernel modules

When developing kernel modules it's often convenient to run edit-compile-run loop as quickly as possible. See below snippet as an example of developing mellanox drivers.

$ nix-build '<nixpkgs>' -A
$ nix-shell '<nixpkgs>' -A linuxPackages.kernel
$ unpackPhase
$ cd linux-*
$ make -C $dev/lib/modules/*/build M=$(pwd)/drivers/net/ethernet/mellanox modules
# insmod ./drivers/net/ethernet/mellanox/mlx5/core/mlx5_core.ko

Chapter 13. Pantheon Destkop

Pantheon is the desktop environment created for the elementary OS distribution. It is written from scratch in Vala, utilizing GNOME technologies with GTK 3 and Granite.

13.1. Enabling Pantheon

All of Pantheon is working in NixOS and the applications should be available, aside from a few exceptions. To enable Pantheon, set

services.xserver.desktopManager.pantheon.enable = true;

This automatically enables LightDM and Pantheon's LightDM greeter. If you'd like to disable this, set

services.xserver.displayManager.lightdm.greeters.pantheon.enable = false;
services.xserver.displayManager.lightdm.enable = false;

but please be aware using Pantheon without LightDM as a display manager will break screenlocking from the UI. The NixOS module for Pantheon installs all of Pantheon's default applications. If you'd like to not install Pantheon's apps, set

services.pantheon.apps.enable = false;

You can also use environment.pantheon.excludePackages to remove any other app (like geary).

13.2. Wingpanel and Switchboard plugins

Wingpanel and Switchboard work differently than they do in other distributions, as far as using plugins. You cannot install a plugin globally (like with environment.systemPackages) to start using it. You should instead be using the following options:

to configure the programs with plugs or indicators.

The difference in NixOS is both these programs are patched to load plugins from a directory that is the value of an environment variable. All of which is controlled in Nix. If you need to configure the particular packages manually you can override the packages like:

wingpanel-with-indicators.override {
  indicators = [

switchboard-with-plugs.override {
  plugs = [

please note that, like how the NixOS options describe these as extra plugins, this would only add to the default plugins included with the programs. If for some reason you'd like to configure which plugins to use exactly, both packages have an argument for this:

wingpanel-with-indicators.override {
  useDefaultIndicators = false;
  indicators = specialListOfIndicators;

switchboard-with-plugs.override {
  useDefaultPlugs = false;
  plugs = specialListOfPlugs;

this could be most useful for testing a particular plug-in in isolation.

13.3. FAQ

I have switched from a different desktop and Pantheon’s theming looks messed up.

Open Switchboard and go to: AdministrationAboutRestore Default SettingsRestore Settings. This will reset any dconf settings to their Pantheon defaults. Note this could reset certain GNOME specific preferences if that desktop was used prior.

I cannot enable both GNOME 3 and Pantheon.

This is a known issue and there is no known workaround.

Does AppCenter work, or is it available?

AppCenter has been available since 20.03, but it is of little use. This is because there is no functioning PackageKit backend for Nix 2.0. In the near future you will be able to install Flatpak applications from AppCenter on NixOS. See this issue.

Chapter 14. Matomo

Matomo is a real-time web analytics application. This module configures php-fpm as backend for Matomo, optionally configuring an nginx vhost as well.

An automatic setup is not suported by Matomo, so you need to configure Matomo itself in the browser-based Matomo setup.

14.1. Database Setup

You also need to configure a MariaDB or MySQL database and -user for Matomo yourself, and enter those credentials in your browser. You can use passwordless database authentication via the UNIX_SOCKET authentication plugin with the following SQL commands:

# For MariaDB
INSTALL PLUGIN unix_socket SONAME 'auth_socket';
CREATE USER 'matomo'@'localhost' IDENTIFIED WITH unix_socket;
GRANT ALL PRIVILEGES ON matomo.* TO 'matomo'@'localhost';

# For MySQL
CREATE USER 'matomo'@'localhost' IDENTIFIED WITH auth_socket;
GRANT ALL PRIVILEGES ON matomo.* TO 'matomo'@'localhost';

Then fill in matomo as database user and database name, and leave the password field blank. This authentication works by allowing only the matomo unix user to authenticate as the matomo database user (without needing a password), but no other users. For more information on passwordless login, see

Of course, you can use password based authentication as well, e.g. when the database is not on the same host.

14.2. Archive Processing

This module comes with the systemd service matomo-archive-processing.service and a timer that automatically triggers archive processing every hour. This means that you can safely disable browser triggers for Matomo archiving at Administration > System > General Settings.

With automatic archive processing, you can now also enable to delete old visitor logs at Administration > System > Privacy, but make sure that you run systemctl start matomo-archive-processing.service at least once without errors if you have already collected data before, so that the reports get archived before the source data gets deleted.

14.3. Backup

You only need to take backups of your MySQL database and the /var/lib/matomo/config/config.ini.php file. Use a user in the matomo group or root to access the file. For more information, see

14.4. Issues

  • Matomo will warn you that the JavaScript tracker is not writable. This is because it's located in the read-only nix store. You can safely ignore this, unless you need a plugin that needs JavaScript tracker access.

14.5. Using other Web Servers than nginx

You can use other web servers by forwarding calls for index.php and piwik.php to the services.phpfpm.pools.<name>.socket fastcgi unix socket. You can use the nginx configuration in the module code as a reference to what else should be configured.

Chapter 15. Nextcloud

Nextcloud is an open-source, self-hostable cloud platform. The server setup can be automated using services.nextcloud. A desktop client is packaged at pkgs.nextcloud-client.

15.1. Basic usage

Nextcloud is a PHP-based application which requires an HTTP server (services.nextcloud optionally supports services.nginx) and a database (it's recommended to use services.postgresql).

A very basic configuration may look like this:

{ pkgs, ... }:
  services.nextcloud = {
    enable = true;
    hostName = "nextcloud.tld";
    nginx.enable = true;
    config = {
      dbtype = "pgsql";
      dbuser = "nextcloud";
      dbhost = "/run/postgresql"; # nextcloud will add /.s.PGSQL.5432 by itself
      dbname = "nextcloud";
      adminpassFile = "/path/to/admin-pass-file";
      adminuser = "root";

  services.postgresql = {
    enable = true;
    ensureDatabases = [ "nextcloud" ];
    ensureUsers = [
     { name = "nextcloud";
       ensurePermissions."DATABASE nextcloud" = "ALL PRIVILEGES";

  # ensure that postgres is running *before* running the setup"nextcloud-setup" = {
    requires = ["postgresql.service"];
    after = ["postgresql.service"];

  networking.firewall.allowedTCPPorts = [ 80 443 ];

The options hostName and nginx.enable are used internally to configure an HTTP server using PHP-FPM and nginx. The config attribute set is used by the imperative installer and all values are written to an additional file to ensure that changes can be applied by changing the module's options.

In case the application serves multiple domains (those are checked with $_SERVER['HTTP_HOST']) it's needed to add them to services.nextcloud.config.extraTrustedDomains.

Auto updates for Nextcloud apps can be enabled using services.nextcloud.autoUpdateApps.

15.2. Pitfalls

Unfortunately Nextcloud appears to be very stateful when it comes to managing its own configuration. The config file lives in the home directory of the nextcloud user (by default /var/lib/nextcloud/config/config.php) and is also used to track several states of the application (e.g. whether installed or not).

All configuration parameters are also stored in /var/lib/nextcloud/config/override.config.php which is generated by the module and linked from the store to ensure that all values from config.php can be modified by the module. However config.php manages the application's state and shouldn't be touched manually because of that.

Warning: Don't delete config.php! This file tracks the application's state and a deletion can cause unwanted side-effects!
Warning: Don't rerun nextcloud-occ maintenance:install! This command tries to install the application and can cause unwanted side-effects!

Nextcloud doesn't allow to move more than one major-version forward. If you're e.g. on v16, you cannot upgrade to v18, you need to upgrade to v17 first. This is ensured automatically as long as the stateVersion is declared properly. In that case the oldest version available (one major behind the one from the previous NixOS release) will be selected by default and the module will generate a warning that reminds the user to upgrade to latest Nextcloud after that deploy.

15.3. Maintainer information

As stated in the previous paragraph, we must provide a clean upgrade-path for Nextcloud since it cannot move more than one major version forward on a single upgrade. This chapter adds some notes how Nextcloud updates should be rolled out in the future.

While minor and patch-level updates are no problem and can be done directly in the package-expression (and should be backported to supported stable branches after that), major-releases should be added in a new attribute (e.g. Nextcloud v19.0.0 should be available in nixpkgs as pkgs.nextcloud19). To provide simple upgrade paths it's generally useful to backport those as well to stable branches. As long as the package-default isn't altered, this won't break existing setups. After that, the versioning-warning in the nextcloud-module should be updated to make sure that the package-option selects the latest version on fresh setups.

If major-releases will be abandoned by upstream, we should check first if those are needed in NixOS for a safe upgrade-path before removing those. In that case we shold keep those packages, but mark them as insecure in an expression like this (in <nixpkgs/pkgs/servers/nextcloud/default.nix>):

/* ... */
  nextcloud17 = generic {
    version = "17.0.x";
    sha256 = "0000000000000000000000000000000000000000000000000000";
    insecure = true;

Chapter 16. Grocy

Grocy is a web-based self-hosted groceries & household management solution for your home.

16.1. Basic usage

A very basic configuration may look like this:

{ pkgs, ... }:
  services.grocy = {
    enable = true;
    hostName = "grocy.tld";

This configures a simple vhost using nginx which listens to grocy.tld with fully configured ACME/LE (this can be disabled by setting services.grocy.nginx.enableSSL to false). After the initial setup the credentials admin:admin can be used to login.

The application's state is persisted at /var/lib/grocy/grocy.db in a sqlite3 database. The migration is applied when requesting the /-route of the application.

16.2. Settings

The configuration for grocy is located at /etc/grocy/config.php. By default, the following settings can be defined in the NixOS-configuration:

{ pkgs, ... }:
  services.grocy.settings = {
    # The default currency in the system for invoices etc.
    # Please note that exchange rates aren't taken into account, this
    # is just the setting for what's shown in the frontend.
    currency = "EUR";

    # The display language (and locale configuration) for grocy.
    culture = "de";

    calendar = {
      # Whether or not to show the week-numbers
      # in the calendar.
      showWeekNumber = true;

      # Index of the first day to be shown in the calendar (0=Sunday, 1=Monday,
      # 2=Tuesday and so on).
      firstDayOfWeek = 2;

If you want to alter the configuration file on your own, you can do this manually with an expression like this:

{ lib, ... }:
  environment.etc."grocy/config.php".text = lib.mkAfter ''
    // Arbitrary PHP code in grocy's configuration file

Chapter 17. Prometheus exporters

Prometheus exporters provide metrics for the prometheus monitoring system.

17.1. Configuration

One of the most common exporters is the node exporter, it provides hardware and OS metrics from the host it's running on. The exporter could be configured as follows:

  services.prometheus.exporters.node = {
    enable = true;
    enabledCollectors = [
    disabledCollectors = [
    openFirewall = true;
    firewallFilter = "-i br0 -p tcp -m tcp --dport 9100";

It should now serve all metrics from the collectors that are explicitly enabled and the ones that are enabled by default, via http under /metrics. In this example the firewall should just allow incoming connections to the exporter's port on the bridge interface br0 (this would have to be configured seperately of course). For more information about configuration see man configuration.nix or search through the available options.

17.2. Adding a new exporter

To add a new exporter, it has to be packaged first (see nixpkgs/pkgs/servers/monitoring/prometheus/ for examples), then a module can be added. The postfix exporter is used in this example:

  • Some default options for all exporters are provided by nixpkgs/nixos/modules/services/monitoring/prometheus/exporters.nix:

    • enable

    • port

    • listenAddress

    • extraFlags

    • openFirewall

    • firewallFilter

    • user

    • group

  • As there is already a package available, the module can now be added. This is accomplished by adding a new file to the nixos/modules/services/monitoring/prometheus/exporters/ directory, which will be called postfix.nix and contains all exporter specific options and configuration:

    # nixpgs/nixos/modules/services/prometheus/exporters/postfix.nix
    { config, lib, pkgs, options }:
    with lib;
      # for convenience we define cfg here
      cfg =;
      port = 9154; # The postfix exporter listens on this port by default
      # `extraOpts` is an attribute set which contains additional options
      # (and optional overrides for default options).
      # Note that this attribute is optional.
      extraOpts = {
        telemetryPath = mkOption {
          type = types.str;
          default = "/metrics";
          description = ''
            Path under which to expose metrics.
        logfilePath = mkOption {
          type = types.path;
          default = /var/log/postfix_exporter_input.log;
          example = /var/log/mail.log;
          description = ''
            Path where Postfix writes log entries.
            This file will be truncated by this exporter!
        showqPath = mkOption {
          type = types.path;
          default = /var/spool/postfix/public/showq;
          example = /var/lib/postfix/queue/public/showq;
          description = ''
            Path at which Postfix places its showq socket.
      # `serviceOpts` is an attribute set which contains configuration
      # for the exporter's systemd service. One of
      # `serviceOpts.script` and `serviceOpts.serviceConfig.ExecStart`
      # has to be specified here. This will be merged with the default
      # service confiuration.
      # Note that by default 'DynamicUser' is 'true'.
      serviceOpts = {
        serviceConfig = {
          DynamicUser = false;
          ExecStart = ''
            ${pkgs.prometheus-postfix-exporter}/bin/postfix_exporter \
              --web.listen-address ${cfg.listenAddress}:${toString cfg.port} \
              --web.telemetry-path ${cfg.telemetryPath} \
              ${concatStringsSep " \\\n  " cfg.extraFlags}

  • This should already be enough for the postfix exporter. Additionally one could now add assertions and conditional default values. This can be done in the 'meta-module' that combines all exporter definitions and generates the submodules: nixpkgs/nixos/modules/services/prometheus/exporters.nix

17.3. Updating an exporter module

Should an exporter option change at some point, it is possible to add information about the change to the exporter definition similar to nixpkgs/nixos/modules/rename.nix:

{ config, lib, pkgs, options }:

with lib;

  cfg =;
  port = 9113;
  extraOpts = {
    # additional module options
    # ...
  serviceOpts = {
    # service configuration
    # ...
  imports = [
    # 'services.prometheus.exporters.nginx.telemetryEndpoint' -> 'services.prometheus.exporters.nginx.telemetryPath'
    (mkRenamedOptionModule [ "telemetryEndpoint" ] [ "telemetryPath" ])

    # removed option 'services.prometheus.exporters.nginx.insecure'
    (mkRemovedOptionModule [ "insecure" ] ''
      This option was replaced by 'prometheus.exporters.nginx.sslVerify' which defaults to true.
    ({ options.warnings = options.warnings; })

Chapter 18. WeeChat

WeeChat is a fast and extensible IRC client.

18.1. Basic Usage

By default, the module creates a systemd unit which runs the chat client in a detached screen session.

This can be done by enabling the weechat service:

{ ... }:

  services.weechat.enable = true;

The service is managed by a dedicated user named weechat in the state directory /var/lib/weechat.

18.2. Re-attaching to WeeChat

WeeChat runs in a screen session owned by a dedicated user. To explicitly allow your another user to attach to this session, the screenrc needs to be tweaked by adding multiuser support:

  programs.screen.screenrc = ''
    multiuser on
    acladd normal_user

Now, the session can be re-attached like this:

screen -x weechat/weechat-screen

The session name can be changed using services.weechat.sessionName.

Chapter 19. Taskserver

Taskserver is the server component of Taskwarrior, a free and open source todo list application.

Upstream documentation:

19.1. Configuration

Taskserver does all of its authentication via TLS using client certificates, so you either need to roll your own CA or purchase a certificate from a known CA, which allows creation of client certificates. These certificates are usually advertised as server certificates.

So in order to make it easier to handle your own CA, there is a helper tool called nixos-taskserver which manages the custom CA along with Taskserver organisations, users and groups.

While the client certificates in Taskserver only authenticate whether a user is allowed to connect, every user has its own UUID which identifies it as an entity.

With nixos-taskserver the client certificate is created along with the UUID of the user, so it handles all of the credentials needed in order to setup the Taskwarrior client to work with a Taskserver.

19.2. The nixos-taskserver tool

Because Taskserver by default only provides scripts to setup users imperatively, the nixos-taskserver tool is used for addition and deletion of organisations along with users and groups defined by services.taskserver.organisations and as well for imperative set up.

The tool is designed to not interfere if the command is used to manually set up some organisations, users or groups.

For example if you add a new organisation using nixos-taskserver org add foo, the organisation is not modified and deleted no matter what you define in services.taskserver.organisations, even if you're adding the same organisation in that option.

The tool is modelled to imitate the official taskd command, documentation for each subcommand can be shown by using the --help switch.

19.3. Declarative/automatic CA management

Everything is done according to what you specify in the module options, however in order to set up a Taskwarrior client for synchronisation with a Taskserver instance, you have to transfer the keys and certificates to the client machine.

This is done using nixos-taskserver user export $orgname $username which is printing a shell script fragment to stdout which can either be used verbatim or adjusted to import the user on the client machine.

For example, let's say you have the following configuration:

  services.taskserver.enable = true;
  services.taskserver.fqdn = "server";
  services.taskserver.listenHost = "::"; = [ "alice" ];

This creates an organisation called my-company with the user alice.

Now in order to import the alice user to another machine alicebox, all we need to do is something like this:

$ ssh server nixos-taskserver user export my-company alice | sh

Of course, if no SSH daemon is available on the server you can also copy & paste it directly into a shell.

After this step the user should be set up and you can start synchronising your tasks for the first time with task sync init on alicebox.

Subsequent synchronisation requests merely require the command task sync after that stage.

19.4. Manual CA management

If you set any options within service.taskserver.pki.manual.*, nixos-taskserver won't issue certificates, but you can still use it for adding or removing user accounts.

Chapter 20. Matrix

Matrix is an open standard for interoperable, decentralised, real-time communication over IP. It can be used to power Instant Messaging, VoIP/WebRTC signalling, Internet of Things communication - or anywhere you need a standard HTTP API for publishing and subscribing to data whilst tracking the conversation history.

This chapter will show you how to set up your own, self-hosted Matrix homeserver using the Synapse reference homeserver, and how to serve your own copy of the Riot web client. See the Try Matrix Now! overview page for links to Riot Apps for Android and iOS, desktop clients, as well as bridges to other networks and other projects around Matrix.

20.1. Synapse Homeserver

Synapse is the reference homeserver implementation of Matrix from the core development team at The following configuration example will set up a synapse server for the domain, served from the host For more information, please refer to the installation instructions of Synapse .

{ pkgs, ... }:
  fqdn =
      join = hostName: domain: hostName + optionalString (domain != null) ".${domain}";
    in join config.networking.hostName config.networking.domain;
in {
  networking = {
    hostName = "myhostname";
    domain = "";
  networking.firewall.allowedTCPPorts = [ 80 443 ];

  services.postgresql.enable = true;
  services.postgresql.initialScript = pkgs.writeText "synapse-init.sql" ''
    CREATE ROLE "matrix-synapse" WITH LOGIN PASSWORD 'synapse';
    CREATE DATABASE "matrix-synapse" WITH OWNER "matrix-synapse"
      TEMPLATE template0
      LC_COLLATE = "C"
      LC_CTYPE = "C";

  services.nginx = {
    enable = true;
    # only recommendedProxySettings and recommendedGzipSettings are strictly required,
    # but the rest make sense as well
    recommendedTlsSettings = true;
    recommendedOptimisation = true;
    recommendedGzipSettings = true;
    recommendedProxySettings = true;

    virtualHosts = {
      # This host section can be placed on a different host than the rest,
      # i.e. to delegate from the host being accessible as ${config.networking.domain}
      # to another host actually running the Matrix homeserver.
      "${config.networking.domain}" = {
        locations."= /.well-known/matrix/server".extraConfig =
            # use 443 instead of the default 8448 port to unite
            # the client-server and server-server port for simplicity
            server = { "m.server" = "${fqdn}:443"; };
          in ''
            add_header Content-Type application/json;
            return 200 '${builtins.toJSON server}';
        locations."= /.well-known/matrix/client".extraConfig =
            client = {
              "m.homeserver" =  { "base_url" = "https://${fqdn}"; };
              "m.identity_server" =  { "base_url" = ""; };
          # ACAO required to allow riot-web on any URL to request this json file
          in ''
            add_header Content-Type application/json;
            add_header Access-Control-Allow-Origin *;
            return 200 '${builtins.toJSON client}';

      # Reverse proxy for Matrix client-server and server-server communication
      ${fqdn} = {
        enableACME = true;
        forceSSL = true;

        # Or do a redirect instead of the 404, or whatever is appropriate for you.
        # But do not put a Matrix Web client here! See the Riot Web section below.
        locations."/".extraConfig = ''
          return 404;

        # forward all Matrix API calls to the synapse Matrix homeserver
        locations."/_matrix" = {
          proxyPass = "http://[::1]:8008"; # without a trailing /
  services.matrix-synapse = {
    enable = true;
    server_name = config.networking.domain;
    listeners = [
        port = 8008;
        bind_address = "::1";
        type = "http";
        tls = false;
        x_forwarded = true;
        resources = [
            names = [ "client" "federation" ];
            compress = false;

If the A and AAAA DNS records on do not point on the same host as the records for, you can easily move the /.well-known virtualHost section of the code to the host that is serving, while the rest stays on with no other changes required. This pattern also allows to seamlessly move the homeserver from to by only changing the /.well-known redirection target.

If you want to run a server with public registration by anybody, you can then enable services.matrix-synapse.enable_registration = true;. Otherwise, or you can generate a registration secret with pwgen -s 64 1 and set it with services.matrix-synapse.registration_shared_secret. To create a new user or admin, run the following after you have set the secret and have rebuilt NixOS:

$ nix run nixpkgs.matrix-synapse
$ register_new_matrix_user -k your-registration-shared-secret http://localhost:8008
New user localpart: your-username
Confirm password:
Make admin [no]:

In the example, this would create a user with the Matrix Identifier Note that the registration secret ends up in the nix store and therefore is world-readable by any user on your machine, so it makes sense to only temporarily activate the registration_shared_secret option until a better solution for NixOS is in place.

20.2. Riot Web Client

Riot Web is the reference web client for Matrix and developed by the core team at The following snippet can be optionally added to the code before to complete the synapse installation with a web client served at and Alternatively, you can use the hosted copy at, or use other web clients or native client applications. Due to the /.well-known urls set up done above, many clients should fill in the required connection details automatically when you enter your Matrix Identifier. See Try Matrix Now! for a list of existing clients and their supported featureset.

  services.nginx.virtualHosts."riot.${fqdn}" = {
    enableACME = true;
    forceSSL = true;
    serverAliases = [

    root = pkgs.riot-web.override {
      conf = {
        default_server_config."m.homeserver" = {
          "base_url" = "${config.networking.domain}";
          "server_name" = "${fqdn}";

Note that the Riot developers do not recommend running Riot and your Matrix homeserver on the same fully-qualified domain name for security reasons. In the example, this means that you should not reuse the virtualHost to also serve Riot, but instead serve it on a different subdomain, like in the example. See the Riot Important Security Notes for more information on this subject.

Chapter 21. Gitlab

Gitlab is a feature-rich git hosting service.

21.1. Prerequisites

The gitlab service exposes only an Unix socket at /run/gitlab/gitlab-workhorse.socket. You need to configure a webserver to proxy HTTP requests to the socket.

For instance, the following configuration could be used to use nginx as frontend proxy:

services.nginx = {
  enable = true;
  recommendedGzipSettings = true;
  recommendedOptimisation = true;
  recommendedProxySettings = true;
  recommendedTlsSettings = true;
  virtualHosts."" = {
    enableACME = true;
    forceSSL = true;
    locations."/".proxyPass = "http://unix:/run/gitlab/gitlab-workhorse.socket";

21.2. Configuring

Gitlab depends on both PostgreSQL and Redis and will automatically enable both services. In the case of PostgreSQL, a database and a role will be created.

The default state dir is /var/gitlab/state. This is where all data like the repositories and uploads will be stored.

A basic configuration with some custom settings could look like this:

services.gitlab = {
  enable = true;
  databasePasswordFile = "/var/keys/gitlab/db_password";
  initialRootPasswordFile = "/var/keys/gitlab/root_password";
  https = true;
  host = "";
  port = 443;
  user = "git";
  group = "git";
  smtp = {
    enable = true;
    address = "localhost";
    port = 25;
  secrets = {
    dbFile = "/var/keys/gitlab/db";
    secretFile = "/var/keys/gitlab/secret";
    otpFile = "/var/keys/gitlab/otp";
    jwsFile = "/var/keys/gitlab/jws";
  extraConfig = {
    gitlab = {
      email_from = "";
      email_display_name = "Example GitLab";
      email_reply_to = "";
      default_projects_features = { builds = false; };

If you're setting up a new Gitlab instance, generate new secrets. You for instance use tr -dc A-Za-z0-9 < /dev/urandom | head -c 128 > /var/keys/gitlab/db to generate a new db secret. Make sure the files can be read by, and only by, the user specified by services.gitlab.user. Gitlab encrypts sensitive data stored in the database. If you're restoring an existing Gitlab instance, you must specify the secrets secret from config/secrets.yml located in your Gitlab state folder.

Refer to Appendix A, Configuration Options for all available configuration options for the services.gitlab module.

21.3. Maintenance

You can run Gitlab's rake tasks with gitlab-rake which will be available on the system when gitlab is enabled. You will have to run the command as the user that you configured to run gitlab with.

For example, to backup a Gitlab instance:

$ sudo -u git -H gitlab-rake gitlab:backup:create

A list of all availabe rake tasks can be obtained by running:

$ sudo -u git -H gitlab-rake -T

Chapter 22. Trezor

Trezor is an open-source cryptocurrency hardware wallet and security token allowing secure storage of private keys.

It offers advanced features such U2F two-factor authorization, SSH login through Trezor SSH agent, GPG and a password manager. For more information, guides and documentation, see

To enable Trezor support, add the following to your configuration.nix:

services.trezord.enable = true;

This will add all necessary udev rules and start Trezor Bridge.

Chapter 23. Emacs

Emacs is an extensible, customizable, self-documenting real-time display editor — and more. At its core is an interpreter for Emacs Lisp, a dialect of the Lisp programming language with extensions to support text editing.

Emacs runs within a graphical desktop environment using the X Window System, but works equally well on a text terminal. Under macOS, a "Mac port" edition is available, which uses Apple's native GUI frameworks.

Nixpkgs provides a superior environment for running Emacs. It's simple to create custom builds by overriding the default packages. Chaotic collections of Emacs Lisp code and extensions can be brought under control using declarative package management. NixOS even provides a systemd user service for automatically starting the Emacs daemon.

23.1. Installing Emacs

Emacs can be installed in the normal way for Nix (see Chapter 6, Package Management). In addition, a NixOS service can be enabled.

23.1.1. The Different Releases of Emacs

Nixpkgs defines several basic Emacs packages. The following are attributes belonging to the pkgs set:

emacs , emacs25

The latest stable version of Emacs 25 using the GTK 2 widget toolkit.


Emacs 25 built without any dependency on X11 libraries.

emacsMacport , emacs25Macport

Emacs 25 with the "Mac port" patches, providing a more native look and feel under macOS.

If those aren't suitable, then the following imitation Emacs editors are also available in Nixpkgs: Zile, mg, Yi, jmacs.

23.1.2. Adding Packages to Emacs

Emacs includes an entire ecosystem of functionality beyond text editing, including a project planner, mail and news reader, debugger interface, calendar, and more.

Most extensions are gotten with the Emacs packaging system (package.el) from Emacs Lisp Package Archive (ELPA), MELPA, MELPA Stable, and Org ELPA. Nixpkgs is regularly updated to mirror all these archives.

Under NixOS, you can continue to use package-list-packages and package-install to install packages. You can also declare the set of Emacs packages you need using the derivations from Nixpkgs. The rest of this section discusses declarative installation of Emacs packages through nixpkgs.

The first step to declare the list of packages you want in your Emacs installation is to create a dedicated derivation. This can be done in a dedicated emacs.nix file such as:

Example 23.1. Nix expression to build Emacs with packages (emacs.nix)

This is a nix expression to build Emacs and some Emacs packages I like
from source on any distribution where Nix is installed. This will install
all the dependencies from the nixpkgs repository and build the binary files
without interfering with the host distribution.

To build the project, type the following from the current directory:

$ nix-build emacs.nix

To run the newly compiled executable:

$ ./result/bin/emacs
{ pkgs ? import <nixpkgs> {} }: 1

  myEmacs = pkgs.emacs; 2
  emacsWithPackages = (pkgs.emacsPackagesGen myEmacs).emacsWithPackages; 3
  emacsWithPackages (epkgs: (with epkgs.melpaStablePackages; [ 4
    magit          # ; Integrate git <C-x g>
    zerodark-theme # ; Nicolas' theme
  ]) ++ (with epkgs.melpaPackages; [ 5
    undo-tree      # ; <C-x u> to show the undo tree
    zoom-frm       # ; increase/decrease font size for all buffers %lt;C-x C-+>
  ]) ++ (with epkgs.elpaPackages; [ 6
    auctex         # ; LaTeX mode
    beacon         # ; highlight my cursor when scrolling
    nameless       # ; hide current package name everywhere in elisp code
  ]) ++ [
    pkgs.notmuch   # From main packages set 7


The first non-comment line in this file ({ pkgs ? ... }) indicates that the whole file represents a function.


The let expression below defines a myEmacs binding pointing to the current stable version of Emacs. This binding is here to separate the choice of the Emacs binary from the specification of the required packages.


This generates an emacsWithPackages function. It takes a single argument: a function from a package set to a list of packages (the packages that will be available in Emacs).


The rest of the file specifies the list of packages to install. In the example, two packages (magit and zerodark-theme) are taken from MELPA stable.


Two packages (undo-tree and zoom-frm) are taken from MELPA.


Three packages are taken from GNU ELPA.


notmuch is taken from a nixpkgs derivation which contains an Emacs mode.

The result of this configuration will be an emacs command which launches Emacs with all of your chosen packages in the load-path.

You can check that it works by executing this in a terminal:

$ nix-build emacs.nix
$ ./result/bin/emacs -q

and then typing M-x package-initialize. Check that you can use all the packages you want in this Emacs instance. For example, try switching to the zerodark theme through M-x load-theme <RET> zerodark <RET> y.


A few popular extensions worth checking out are: auctex, company, edit-server, flycheck, helm, iedit, magit, multiple-cursors, projectile, and yasnippet.

The list of available packages in the various ELPA repositories can be seen with the following commands:

Example 23.2. Querying Emacs packages

nix-env -f "<nixpkgs>" -qaP -A emacsPackages.elpaPackages
nix-env -f "<nixpkgs>" -qaP -A emacsPackages.melpaPackages
nix-env -f "<nixpkgs>" -qaP -A emacsPackages.melpaStablePackages
nix-env -f "<nixpkgs>" -qaP -A emacsPackages.orgPackages

If you are on NixOS, you can install this particular Emacs for all users by adding it to the list of system packages (see Section 6.1, “Declarative Package Management”). Simply modify your file configuration.nix to make it contain:

Example 23.3. Custom Emacs in configuration.nix

 environment.systemPackages = [
   # [...]
   (import /path/to/emacs.nix { inherit pkgs; })

In this case, the next nixos-rebuild switch will take care of adding your emacs to the PATH environment variable (see Chapter 3, Changing the Configuration).

If you are not on NixOS or want to install this particular Emacs only for yourself, you can do so by adding it to your ~/.config/nixpkgs/config.nix (see Nixpkgs manual):

Example 23.4. Custom Emacs in ~/.config/nixpkgs/config.nix

  packageOverrides = super: let self = super.pkgs; in {
    myemacs = import /path/to/emacs.nix { pkgs = self; };

In this case, the next nix-env -f '<nixpkgs>' -iA myemacs will take care of adding your emacs to the PATH environment variable.

23.1.3. Advanced Emacs Configuration

If you want, you can tweak the Emacs package itself from your emacs.nix. For example, if you want to have a GTK 3-based Emacs instead of the default GTK 2-based binary and remove the automatically generated emacs.desktop (useful is you only use emacsclient), you can change your file emacs.nix in this way:

Example 23.5. Custom Emacs build

{ pkgs ? import <nixpkgs> {} }:
  myEmacs = (pkgs.emacs.override {
    # Use gtk3 instead of the default gtk2
    withGTK3 = true;
    withGTK2 = false;
  }).overrideAttrs (attrs: {
    # I don't want emacs.desktop file because I only use
    # emacsclient.
    postInstall = (attrs.postInstall or "") + ''
      rm $out/share/applications/emacs.desktop
in [...]

After building this file as shown in Example 23.1, “Nix expression to build Emacs with packages (emacs.nix)”, you will get an GTK 3-based Emacs binary pre-loaded with your favorite packages.

23.2. Running Emacs as a Service

NixOS provides an optional systemd service which launches Emacs daemon with the user's login session.

Source: modules/services/editors/emacs.nix

23.2.1. Enabling the Service

To install and enable the systemd user service for Emacs daemon, add the following to your configuration.nix:

services.emacs.enable = true;
services.emacs.package = import /home/cassou/.emacs.d { pkgs = pkgs; };

The services.emacs.package option allows a custom derivation to be used, for example, one created by emacsWithPackages.

Ensure that the Emacs server is enabled for your user's Emacs configuration, either by customizing the server-mode variable, or by adding (server-start) to ~/.emacs.d/init.el.

To start the daemon, execute the following:

$ nixos-rebuild switch  # to activate the new configuration.nix
$ systemctl --user daemon-reload        # to force systemd reload
$ systemctl --user start emacs.service  # to start the Emacs daemon

The server should now be ready to serve Emacs clients.

23.2.2. Starting the client

Ensure that the emacs server is enabled, either by customizing the server-mode variable, or by adding (server-start) to ~/.emacs.

To connect to the emacs daemon, run one of the following:

emacsclient FILENAME
emacsclient --create-frame  # opens a new frame (window)
emacsclient --create-frame --tty  # opens a new frame on the current terminal

23.2.3. Configuring the EDITOR variable

If services.emacs.defaultEditor is true, the EDITOR variable will be set to a wrapper script which launches emacsclient.

Any setting of EDITOR in the shell config files will override services.emacs.defaultEditor. To make sure EDITOR refers to the Emacs wrapper script, remove any existing EDITOR assignment from .profile, .bashrc, .zshenv or any other shell config file.

If you have formed certain bad habits when editing files, these can be corrected with a shell alias to the wrapper script:

alias vi=$EDITOR

23.2.4. Per-User Enabling of the Service

In general, systemd user services are globally enabled by symlinks in /etc/systemd/user. In the case where Emacs daemon is not wanted for all users, it is possible to install the service but not globally enable it:

services.emacs.enable = false;
services.emacs.install = true;

To enable the systemd user service for just the currently logged in user, run:

systemctl --user enable emacs

This will add the symlink ~/.config/systemd/user/emacs.service.

23.3. Configuring Emacs

The Emacs init file should be changed to load the extension packages at startup:

Example 23.6. Package initialization in .emacs

(require 'package)

;; optional. makes unpure packages archives unavailable
(setq package-archives nil)

(setq package-enable-at-startup nil)

After the declarative emacs package configuration has been tested, previously downloaded packages can be cleaned up by removing ~/.emacs.d/elpa (do make a backup first, in case you forgot a package).

23.3.1. A Major Mode for Nix Expressions

Of interest may be melpaPackages.nix-mode, which provides syntax highlighting for the Nix language. This is particularly convenient if you regularly edit Nix files.

23.3.2. Accessing man pages

You can use woman to get completion of all available man pages. For example, type M-x woman <RET> nixos-rebuild <RET>.

23.3.3. Editing DocBook 5 XML Documents

Emacs includes nXML, a major-mode for validating and editing XML documents. When editing DocBook 5.0 documents, such as this one, nXML needs to be configured with the relevant schema, which is not included.

To install the DocBook 5.0 schemas, either add pkgs.docbook5 to environment.systemPackages (NixOS), or run nix-env -f '<nixpkgs>' -iA docbook5 (Nix).

Then customize the variable rng-schema-locating-files to include ~/.emacs.d/schemas.xml and put the following text into that file:

Example 23.7. nXML Schema Configuration (~/.emacs.d/schemas.xml)

<?xml version="1.0"?>
  To let emacs find this file, evaluate:
  (add-to-list 'rng-schema-locating-files "~/.emacs.d/schemas.xml")
<locatingRules xmlns="">
    Use this variation if pkgs.docbook5 is added to environment.systemPackages
  <namespace ns=""
    Use this variation if installing schema with "nix-env -iA pkgs.docbook5".
  <namespace ns=""

Chapter 24. Flatpak

Source: modules/services/desktop/flatpak.nix

Upstream documentation:

Flatpak is a system for building, distributing, and running sandboxed desktop applications on Linux.

To enable Flatpak, add the following to your configuration.nix:

  services.flatpak.enable = true;

For the sandboxed apps to work correctly, desktop integration portals need to be installed. If you run GNOME, this will be handled automatically for you; in other cases, you will need to add something like the following to your configuration.nix:

  xdg.portal.extraPortals = [ pkgs.xdg-desktop-portal-gtk ];

Then, you will need to add a repository, for example, Flathub, either using the following commands:

$ flatpak remote-add --if-not-exists flathub
$ flatpak update

or by opening the repository file in GNOME Software.

Finally, you can search and install programs:

$ flatpak search bustle
$ flatpak install flathub org.freedesktop.Bustle
$ flatpak run org.freedesktop.Bustle

Again, GNOME Software offers graphical interface for these tasks.

Chapter 25. PostgreSQL

Source: modules/services/databases/postgresql.nix

Upstream documentation:

PostgreSQL is an advanced, free relational database.

25.1. Configuring

To enable PostgreSQL, add the following to your configuration.nix:

services.postgresql.enable = true;
services.postgresql.package = pkgs.postgresql_11;

Note that you are required to specify the desired version of PostgreSQL (e.g. pkgs.postgresql_11). Since upgrading your PostgreSQL version requires a database dump and reload (see below), NixOS cannot provide a default value for services.postgresql.package such as the most recent release of PostgreSQL.

By default, PostgreSQL stores its databases in /var/lib/postgresql/$psqlSchema. You can override this using services.postgresql.dataDir, e.g.

services.postgresql.dataDir = "/data/postgresql";

25.2. Upgrading

Major PostgreSQL upgrade requires PostgreSQL downtime and a few imperative steps to be called. To simplify this process, use the following NixOS module: = {
    enable = true;
    package = pkgs.postgresql_12;
    ## set a custom new dataDir
    # dataDir = "/some/data/dir";
  environment.systemPackages =
    let newpg =;
    in [
      (pkgs.writeScriptBin "upgrade-pg-cluster" ''
        set -x
        export OLDDATA="${}"
        export NEWDATA="${newpg.dataDir}"
        export OLDBIN="${}/bin"
        export NEWBIN="${newpg.package}/bin"

        install -d -m 0700 -o postgres -g postgres "$NEWDATA"
        cd "$NEWDATA"
        sudo -u postgres $NEWBIN/initdb -D "$NEWDATA"

        systemctl stop postgresql    # old one

        sudo -u postgres $NEWBIN/pg_upgrade \
          --old-datadir "$OLDDATA" --new-datadir "$NEWDATA" \
          --old-bindir $OLDBIN --new-bindir $NEWBIN \

The upgrade process is:

  1. Rebuild nixos configuration with the configuration above added to your configuration.nix. Alternatively, add that into separate file and reference it in imports list.

  2. Login as root (sudo su -)

  3. Run upgrade-pg-cluster. It will stop old postgresql, initialize new one and migrate old one to new one. You may supply arguments like --jobs 4 and --link to speedup migration process. See for details.

  4. Change postgresql package in NixOS configuration to the one you were upgrading to, and change dataDir to the one you have migrated to. Rebuild NixOS. This should start new postgres using upgraded data directory.

  5. After upgrade you may want to ANALYZE new db.

25.3. Options

A complete list of options for the PostgreSQL module may be found here.

25.4. Plugins

Plugins collection for each PostgreSQL version can be accessed with .pkgs. For example, for pkgs.postgresql_11 package, its plugin collection is accessed by pkgs.postgresql_11.pkgs:

$ nix repl '<nixpkgs>'

Loading '<nixpkgs>'...
Added 10574 variables.

nix-repl> postgresql_11.pkgs.<TAB><TAB>
postgresql_11.pkgs.cstore_fdw        postgresql_11.pkgs.pg_repack
postgresql_11.pkgs.pg_auto_failover  postgresql_11.pkgs.pg_safeupdate
postgresql_11.pkgs.pg_bigm           postgresql_11.pkgs.pg_similarity
postgresql_11.pkgs.pg_cron           postgresql_11.pkgs.pg_topn
postgresql_11.pkgs.pg_hll            postgresql_11.pkgs.pgjwt
postgresql_11.pkgs.pg_partman        postgresql_11.pkgs.pgroonga

To add plugins via NixOS configuration, set services.postgresql.extraPlugins:

services.postgresql.package = pkgs.postgresql_11;
services.postgresql.extraPlugins = with pkgs.postgresql_11.pkgs; [

You can build custom PostgreSQL-with-plugins (to be used outside of NixOS) using function .withPackages. For example, creating a custom PostgreSQL package in an overlay can look like:

self: super: {
  postgresql_custom = self.postgresql_11.withPackages (ps: [

Here's a recipe on how to override a particular plugin through an overlay:

self: super: {
  postgresql_11 = super.postgresql_11.override { this = self.postgresql_11; } // {
    pkgs = super.postgresql_11.pkgs // {
      pg_repack = super.postgresql_11.pkgs.pg_repack.overrideAttrs (_: {
        name = "pg_repack-v20181024";
        src = self.fetchzip {
          url = "";
          sha256 = "17k6hq9xaax87yz79j773qyigm4fwk8z4zh5cyp6z0sxnwfqxxw5";

Chapter 26. FoundationDB

Source: modules/services/databases/foundationdb.nix

Upstream documentation:

Maintainer: Austin Seipp

Available version(s): 5.1.x, 5.2.x, 6.0.x

FoundationDB (or "FDB") is an open source, distributed, transactional key-value store.

26.1. Configuring and basic setup

To enable FoundationDB, add the following to your configuration.nix:

services.foundationdb.enable = true;
services.foundationdb.package = pkgs.foundationdb52; # FoundationDB 5.2.x

The services.foundationdb.package option is required, and must always be specified. Due to the fact FoundationDB network protocols and on-disk storage formats may change between (major) versions, and upgrades must be explicitly handled by the user, you must always manually specify this yourself so that the NixOS module will use the proper version. Note that minor, bugfix releases are always compatible.

After running nixos-rebuild, you can verify whether FoundationDB is running by executing fdbcli (which is added to environment.systemPackages):

$ sudo -u foundationdb fdbcli
Using cluster file `/etc/foundationdb/fdb.cluster'.

The database is available.

Welcome to the fdbcli. For help, type `help'.
fdb> status

Using cluster file `/etc/foundationdb/fdb.cluster'.

  Redundancy mode        - single
  Storage engine         - memory
  Coordinators           - 1

  FoundationDB processes - 1
  Machines               - 1
  Memory availability    - 5.4 GB per process on machine with least available
  Fault Tolerance        - 0 machines
  Server time            - 04/20/18 15:21:14



You can also write programs using the available client libraries. For example, the following Python program can be run in order to grab the cluster status, as a quick example. (This example uses nix-shell shebang support to automatically supply the necessary Python modules).

a@link> cat
#! /usr/bin/env nix-shell
#! nix-shell -i python -p python pythonPackages.foundationdb52

import fdb
import json

def main():
    db =

    def get_status(tr):
        return str(tr['\xff\xff/status/json'])

    obj = json.loads(get_status(db))
    print('FoundationDB available: %s' % obj['client']['database_status']['available'])

if __name__ == "__main__":
a@link> chmod +x
a@link> ./
FoundationDB available: True

FoundationDB is run under the foundationdb user and group by default, but this may be changed in the NixOS configuration. The systemd unit foundationdb.service controls the fdbmonitor process.

By default, the NixOS module for FoundationDB creates a single SSD-storage based database for development and basic usage. This storage engine is designed for SSDs and will perform poorly on HDDs; however it can handle far more data than the alternative "memory" engine and is a better default choice for most deployments. (Note that you can change the storage backend on-the-fly for a given FoundationDB cluster using fdbcli.)

Furthermore, only 1 server process and 1 backup agent are started in the default configuration. See below for more on scaling to increase this.

FoundationDB stores all data for all server processes under /var/lib/foundationdb. You can override this using services.foundationdb.dataDir, e.g.

services.foundationdb.dataDir = "/data/fdb";

Similarly, logs are stored under /var/log/foundationdb by default, and there is a corresponding services.foundationdb.logDir as well.

26.2. Scaling processes and backup agents

Scaling the number of server processes is quite easy; simply specify services.foundationdb.serverProcesses to be the number of FoundationDB worker processes that should be started on the machine.

FoundationDB worker processes typically require 4GB of RAM per-process at minimum for good performance, so this option is set to 1 by default since the maximum amount of RAM is unknown. You're advised to abide by this restriction, so pick a number of processes so that each has 4GB or more.

A similar option exists in order to scale backup agent processes, services.foundationdb.backupProcesses. Backup agents are not as performance/RAM sensitive, so feel free to experiment with the number of available backup processes.

26.3. Clustering

FoundationDB on NixOS works similarly to other Linux systems, so this section will be brief. Please refer to the full FoundationDB documentation for more on clustering.

FoundationDB organizes clusters using a set of coordinators, which are just specially-designated worker processes. By default, every installation of FoundationDB on NixOS will start as its own individual cluster, with a single coordinator: the first worker process on localhost.

Coordinators are specified globally using the /etc/foundationdb/fdb.cluster file, which all servers and client applications will use to find and join coordinators. Note that this file can not be managed by NixOS so easily: FoundationDB is designed so that it will rewrite the file at runtime for all clients and nodes when cluster coordinators change, with clients transparently handling this without intervention. It is fundamentally a mutable file, and you should not try to manage it in any way in NixOS.

When dealing with a cluster, there are two main things you want to do:

  • Add a node to the cluster for storage/compute.

  • Promote an ordinary worker to a coordinator.

A node must already be a member of the cluster in order to properly be promoted to a coordinator, so you must always add it first if you wish to promote it.

To add a machine to a FoundationDB cluster:

  • Choose one of the servers to start as the initial coordinator.

  • Copy the /etc/foundationdb/fdb.cluster file from this server to all the other servers. Restart FoundationDB on all of these other servers, so they join the cluster.

  • All of these servers are now connected and working together in the cluster, under the chosen coordinator.

At this point, you can add as many nodes as you want by just repeating the above steps. By default there will still be a single coordinator: you can use fdbcli to change this and add new coordinators.

As a convenience, FoundationDB can automatically assign coordinators based on the redundancy mode you wish to achieve for the cluster. Once all the nodes have been joined, simply set the replication policy, and then issue the coordinators auto command

For example, assuming we have 3 nodes available, we can enable double redundancy mode, then auto-select coordinators. For double redundancy, 3 coordinators is ideal: therefore FoundationDB will make every node a coordinator automatically:

fdbcli> configure double ssd
fdbcli> coordinators auto

This will transparently update all the servers within seconds, and appropriately rewrite the fdb.cluster file, as well as informing all client processes to do the same.

26.4. Client connectivity

By default, all clients must use the current fdb.cluster file to access a given FoundationDB cluster. This file is located by default in /etc/foundationdb/fdb.cluster on all machines with the FoundationDB service enabled, so you may copy the active one from your cluster to a new node in order to connect, if it is not part of the cluster.

26.5. Client authorization and TLS

By default, any user who can connect to a FoundationDB process with the correct cluster configuration can access anything. FoundationDB uses a pluggable design to transport security, and out of the box it supports a LibreSSL-based plugin for TLS support. This plugin not only does in-flight encryption, but also performs client authorization based on the given endpoint's certificate chain. For example, a FoundationDB server may be configured to only accept client connections over TLS, where the client TLS certificate is from organization Acme Co in the Research and Development unit.

Configuring TLS with FoundationDB is done using the services.foundationdb.tls options in order to control the peer verification string, as well as the certificate and its private key.

Note that the certificate and its private key must be accessible to the FoundationDB user account that the server runs under. These files are also NOT managed by NixOS, as putting them into the store may reveal private information.

After you have a key and certificate file in place, it is not enough to simply set the NixOS module options -- you must also configure the fdb.cluster file to specify that a given set of coordinators use TLS. This is as simple as adding the suffix :tls to your cluster coordinator configuration, after the port number. For example, assuming you have a coordinator on localhost with the default configuration, simply specifying:


will configure all clients and server processes to use TLS from now on.

26.6. Backups and Disaster Recovery

The usual rules for doing FoundationDB backups apply on NixOS as written in the FoundationDB manual. However, one important difference is the security profile for NixOS: by default, the foundationdb systemd unit uses Linux namespaces to restrict write access to the system, except for the log directory, data directory, and the /etc/foundationdb/ directory. This is enforced by default and cannot be disabled.

However, a side effect of this is that the fdbbackup command doesn't work properly for local filesystem backups: FoundationDB uses a server process alongside the database processes to perform backups and copy the backups to the filesystem. As a result, this process is put under the restricted namespaces above: the backup process can only write to a limited number of paths.

In order to allow flexible backup locations on local disks, the FoundationDB NixOS module supports a services.foundationdb.extraReadWritePaths option. This option takes a list of paths, and adds them to the systemd unit, allowing the processes inside the service to write (and read) the specified directories.

For example, to create backups in /opt/fdb-backups, first set up the paths in the module options:

services.foundationdb.extraReadWritePaths = [ "/opt/fdb-backups" ];

Restart the FoundationDB service, and it will now be able to write to this directory (even if it does not yet exist.) Note: this path must exist before restarting the unit. Otherwise, systemd will not include it in the private FoundationDB namespace (and it will not add it dynamically at runtime).

You can now perform a backup:

$ sudo -u foundationdb fdbbackup start  -t default -d file:///opt/fdb-backups
$ sudo -u foundationdb fdbbackup status -t default

26.7. Known limitations

The FoundationDB setup for NixOS should currently be considered beta. FoundationDB is not new software, but the NixOS compilation and integration has only undergone fairly basic testing of all the available functionality.

  • There is no way to specify individual parameters for individual fdbserver processes. Currently, all server processes inherit all the global fdbmonitor settings.

  • Ruby bindings are not currently installed.

  • Go bindings are not currently installed.

26.8. Options

NixOS's FoundationDB module allows you to configure all of the most relevant configuration options for fdbmonitor, matching it quite closely. A complete list of options for the FoundationDB module may be found here. You should also read the FoundationDB documentation as well.

26.9. Full documentation

FoundationDB is a complex piece of software, and requires careful administration to properly use. Full documentation for administration can be found here:

Chapter 27. Hiding process information


security.hideProcessInformation = true;

ensures that access to process information is restricted to the owning user. This implies, among other things, that command-line arguments remain private. Unless your deployment relies on unprivileged users being able to inspect the process information of other users, this option should be safe to enable.

Members of the proc group are exempt from process information hiding.

To allow a service foo to run without process information hiding, set = [ "proc" ];

Chapter 28. SSL/TLS Certificates with ACME

NixOS supports automatic domain validation & certificate retrieval and renewal using the ACME protocol. This is currently only implemented by and for Let's Encrypt. The alternative ACME client lego is used under the hood.

28.1. Prerequisites

You need to have a running HTTP server for verification. The server must have a webroot defined that can serve .well-known/acme-challenge. This directory must be writeable by the user that will run the ACME client.

For instance, this generic snippet could be used for Nginx:

http {
  server {
    server_name _;
    listen 80;
    listen [::]:80;

    location /.well-known/acme-challenge {
      root /var/www/challenges;

    location / {
      return 301 https://$host$request_uri;

28.2. Configuring

To enable ACME certificate retrieval & renewal for a certificate for, add the following in your configuration.nix:

security.acme.certs."" = {
  webroot = "/var/www/challenges";
  email = "";

The private key key.pem and certificate fullchain.pem will be put into /var/lib/acme/

Refer to Appendix A, Configuration Options for all available configuration options for the security.acme module.

28.3. Using ACME certificates in Nginx

NixOS supports fetching ACME certificates for you by setting enableACME = true; in a virtualHost config. We first create self-signed placeholder certificates in place of the real ACME certs. The placeholder certs are overwritten when the ACME certs arrive. For the config would look like.

services.nginx = {
  enable = true;
  virtualHosts = {
    "" = {
      forceSSL = true;
      enableACME = true;
      locations."/" = {
        root = "/var/www";

Chapter 29. Oh my ZSH

oh-my-zsh is a framework to manage your ZSH configuration including completion scripts for several CLI tools or custom prompt themes.

29.1. Basic usage

The module uses the oh-my-zsh package with all available features. The initial setup using Nix expressions is fairly similar to the configuration format of oh-my-zsh.

  programs.zsh.ohMyZsh = {
    enable = true;
    plugins = [ "git" "python" "man" ];
    theme = "agnoster";

For a detailed explanation of these arguments please refer to the oh-my-zsh docs.

The expression generates the needed configuration and writes it into your /etc/zshrc.

29.2. Custom additions

Sometimes third-party or custom scripts such as a modified theme may be needed. oh-my-zsh provides the ZSH_CUSTOM environment variable for this which points to a directory with additional scripts.

The module can do this as well:

  programs.zsh.ohMyZsh.custom = "~/path/to/custom/scripts";

29.3. Custom environments

There are several extensions for oh-my-zsh packaged in nixpkgs. One of them is nix-zsh-completions which bundles completion scripts and a plugin for oh-my-zsh.

Rather than using a single mutable path for ZSH_CUSTOM, it's also possible to generate this path from a list of Nix packages:

{ pkgs, ... }:
  programs.zsh.ohMyZsh.customPkgs = with pkgs; [
    # and even more...

Internally a single store path will be created using buildEnv. Please refer to the docs of buildEnv for further reference.

Please keep in mind that this is not compatible with programs.zsh.ohMyZsh.custom as it requires an immutable store path while custom shall remain mutable! An evaluation failure will be thrown if both custom and customPkgs are set.

29.4. Package your own customizations

If third-party customizations (e.g. new themes) are supposed to be added to oh-my-zsh there are several pitfalls to keep in mind:

  • To comply with the default structure of ZSH the entire output needs to be written to $out/share/zsh.

  • Completion scripts are supposed to be stored at $out/share/zsh/site-functions. This directory is part of the fpath and the package should be compatible with pure ZSH setups. The module will automatically link the contents of site-functions to completions directory in the proper store path.

  • The plugins directory needs the structure pluginname/pluginname.plugin.zsh as structured in the upstream repo.

A derivation for oh-my-zsh may look like this:

{ stdenv, fetchFromGitHub }:

stdenv.mkDerivation rec {
  name = "exemplary-zsh-customization-${version}";
  version = "1.0.0";
  src = fetchFromGitHub {
    # path to the upstream repository

  dontBuild = true;
  installPhase = ''
    mkdir -p $out/share/zsh/site-functions
    cp {themes,plugins} $out/share/zsh
    cp completions $out/share/zsh/site-functions

Chapter 30. Plotinus

Source: modules/programs/plotinus.nix

Upstream documentation:

Plotinus is a searchable command palette in every modern GTK application.

When in a GTK 3 application and Plotinus is enabled, you can press Ctrl+Shift+P to open the command palette. The command palette provides a searchable list of of all menu items in the application.

To enable Plotinus, add the following to your configuration.nix:

programs.plotinus.enable = true;

Chapter 31. Digital Bitbox

Digital Bitbox is a hardware wallet and second-factor authenticator.

The digitalbitbox programs module may be installed by setting programs.digitalbitbox to true in a manner similar to

programs.digitalbitbox.enable = true;

and bundles the digitalbitbox package (see Section 31.1, “Package”), which contains the dbb-app and dbb-cli binaries, along with the hardware module (see Section 31.2, “Hardware”) which sets up the necessary udev rules to access the device.

Enabling the digitalbitbox module is pretty much the easiest way to get a Digital Bitbox device working on your system.

For more information, see

31.1. Package

The binaries, dbb-app (a GUI tool) and dbb-cli (a CLI tool), are available through the digitalbitbox package which could be installed as follows:

environment.systemPackages = [

31.2. Hardware

The digitalbitbox hardware package enables the udev rules for Digital Bitbox devices and may be installed as follows:

hardware.digitalbitbox.enable = true;

In order to alter the udev rules, one may provide different values for the udevRule51 and udevRule52 attributes by means of overriding as follows:

programs.digitalbitbox = {
  enable = true;
  package = pkgs.digitalbitbox.override {
    udevRule51 = "something else";

Chapter 32. Input Methods

Input methods are an operating system component that allows any data, such as keyboard strokes or mouse movements, to be received as input. In this way users can enter characters and symbols not found on their input devices. Using an input method is obligatory for any language that has more graphemes than there are keys on the keyboard.

The following input methods are available in NixOS:

  • IBus: The intelligent input bus.

  • Fcitx: A customizable lightweight input method.

  • Nabi: A Korean input method based on XIM.

  • Uim: The universal input method, is a library with a XIM bridge.

32.1. IBus

IBus is an Intelligent Input Bus. It provides full featured and user friendly input method user interface.

The following snippet can be used to configure IBus:

i18n.inputMethod = {
  enabled = "ibus";
  ibus.engines = with pkgs.ibus-engines; [ anthy hangul mozc ];

i18n.inputMethod.ibus.engines is optional and can be used to add extra IBus engines.

Available extra IBus engines are:

  • Anthy (ibus-engines.anthy): Anthy is a system for Japanese input method. It converts Hiragana text to Kana Kanji mixed text.

  • Hangul (ibus-engines.hangul): Korean input method.

  • m17n (ibus-engines.m17n): m17n is an input method that uses input methods and corresponding icons in the m17n database.

  • mozc (ibus-engines.mozc): A Japanese input method from Google.

  • Table (ibus-engines.table): An input method that load tables of input methods.

  • table-others (ibus-engines.table-others): Various table-based input methods. To use this, and any other table-based input methods, it must appear in the list of engines along with table. For example:

    ibus.engines = with pkgs.ibus-engines; [ table table-others ];

To use any input method, the package must be added in the configuration, as shown above, and also (after running nixos-rebuild) the input method must be added from IBus' preference dialog.


If IBus works in some applications but not others, a likely cause of this is that IBus is depending on a different version of glib to what the applications are depending on. This can be checked by running nix-store -q --requisites <path> | grep glib, where <path> is the path of either IBus or an application in the Nix store. The glib packages must match exactly. If they do not, uninstalling and reinstalling the application is a likely fix.

32.2. Fcitx

Fcitx is an input method framework with extension support. It has three built-in Input Method Engine, Pinyin, QuWei and Table-based input methods.

The following snippet can be used to configure Fcitx:

i18n.inputMethod = {
  enabled = "fcitx";
  fcitx.engines = with pkgs.fcitx-engines; [ mozc hangul m17n ];

i18n.inputMethod.fcitx.engines is optional and can be used to add extra Fcitx engines.

Available extra Fcitx engines are:

  • Anthy (fcitx-engines.anthy): Anthy is a system for Japanese input method. It converts Hiragana text to Kana Kanji mixed text.

  • Chewing (fcitx-engines.chewing): Chewing is an intelligent Zhuyin input method. It is one of the most popular input methods among Traditional Chinese Unix users.

  • Hangul (fcitx-engines.hangul): Korean input method.

  • Unikey (fcitx-engines.unikey): Vietnamese input method.

  • m17n (fcitx-engines.m17n): m17n is an input method that uses input methods and corresponding icons in the m17n database.

  • mozc (fcitx-engines.mozc): A Japanese input method from Google.

  • table-others (fcitx-engines.table-others): Various table-based input methods.

32.3. Nabi

Nabi is an easy to use Korean X input method. It allows you to enter phonetic Korean characters (hangul) and pictographic Korean characters (hanja).

The following snippet can be used to configure Nabi:

i18n.inputMethod = {
  enabled = "nabi";

32.4. Uim

Uim (short for "universal input method") is a multilingual input method framework. Applications can use it through so-called bridges.

The following snippet can be used to configure uim:

i18n.inputMethod = {
  enabled = "uim";

Note: The i18n.inputMethod.uim.toolbar option can be used to choose uim toolbar.

Chapter 33. Profiles

In some cases, it may be desirable to take advantage of commonly-used, predefined configurations provided by nixpkgs, but different from those that come as default. This is a role fulfilled by NixOS's Profiles, which come as files living in <nixpkgs/nixos/modules/profiles>. That is to say, expected usage is to add them to the imports list of your /etc/configuration.nix as such:

  imports = [

Even if some of these profiles seem only useful in the context of install media, many are actually intended to be used in real installs.

What follows is a brief explanation on the purpose and use-case for each profile. Detailing each option configured by each one is out of scope.

33.1. All Hardware

Enables all hardware supported by NixOS: i.e., all firmware is included, and all devices from which one may boot are enabled in the initrd. Its primary use is in the NixOS installation CDs.

The enabled kernel modules include support for SATA and PATA, SCSI (partially), USB, Firewire (untested), Virtio (QEMU, KVM, etc.), VMware, and Hyper-V. Additionally, hardware.enableAllFirmware is enabled, and the firmware for the ZyDAS ZD1211 chipset is specifically installed.

33.2. Base

Defines the software packages included in the "minimal" installation CD. It installs several utilities useful in a simple recovery or install media, such as a text-mode web browser, and tools for manipulating block devices, networking, hardware diagnostics, and filesystems (with their respective kernel modules).

33.3. Clone Config

This profile is used in installer images. It provides an editable configuration.nix that imports all the modules that were also used when creating the image in the first place. As a result it allows users to edit and rebuild the live-system.

On images where the installation media also becomes an installation target, copying over configuration.nix should be disabled by setting installer.cloneConfig to false. For example, this is done in sd-image-aarch64.nix.

33.4. Demo

This profile just enables a demo user, with password demo, uid 1000, wheel group and autologin in the SDDM display manager.

33.5. Docker Container

This is the profile from which the Docker images are generated. It prepares a working system by importing the Minimal and Clone Config profiles, and setting appropriate configuration options that are useful inside a container context, like boot.isContainer.

33.6. Graphical

Defines a NixOS configuration with the Plasma 5 desktop. It's used by the graphical installation CD.

It sets services.xserver.enable, services.xserver.displayManager.sddm.enable, services.xserver.desktopManager.plasma5.enable, and services.xserver.libinput.enable to true. It also includes glxinfo and firefox in the system packages list.

33.7. Hardened

A profile with most (vanilla) hardening options enabled by default, potentially at the cost of features and performance.

This includes a hardened kernel, and limiting the system information available to processes through the /sys and /proc filesystems. It also disables the User Namespaces feature of the kernel, which stops Nix from being able to build anything (this particular setting can be overriden via security.allowUserNamespaces). See the profile source for further detail on which settings are altered.

33.8. Headless

Common configuration for headless machines (e.g., Amazon EC2 instances).

Disables sound, vesa, serial consoles, emergency mode, grub splash images and configures the kernel to reboot automatically on panic.

33.9. Installation Device

Provides a basic configuration for installation devices like CDs. This enables redistributable firmware, includes the Clone Config profile and a copy of the Nixpkgs channel, so nixos-install works out of the box.

Documentation for Nixpkgs and NixOS are forcefully enabled (to override the Minimal profile preference); the NixOS manual is shown automatically on TTY 8, udisks is disabled. Autologin is enabled as nixos user, while passwordless login as both root and nixos is possible. Passwordless sudo is enabled too. wpa_supplicant is enabled, but configured to not autostart.

It is explained how to login, start the ssh server, and if available, how to start the display manager.

Several settings are tweaked so that the installer has a better chance of succeeding under low-memory environments.

33.10. Minimal

This profile defines a small NixOS configuration. It does not contain any graphical stuff. It's a very short file that enables noXlibs, sets i18n.supportedLocales to only support the user-selected locale, disables packages' documentation , and disables sound.

33.11. QEMU Guest

This profile contains common configuration for virtual machines running under QEMU (using virtio).

It makes virtio modules available on the initrd, sets the system time from the hardware clock to work around a bug in qemu-kvm, and enables rngd.

Chapter 34. Kubernetes

The NixOS Kubernetes module is a collective term for a handful of individual submodules implementing the Kubernetes cluster components.

There are generally two ways of enabling Kubernetes on NixOS. One way is to enable and configure cluster components appropriately by hand:

services.kubernetes = {
  apiserver.enable = true;
  controllerManager.enable = true;
  scheduler.enable = true;
  addonManager.enable = true;
  proxy.enable = true;
  flannel.enable = true;

Another way is to assign cluster roles ("master" and/or "node") to the host. This enables apiserver, controllerManager, scheduler, addonManager, kube-proxy and etcd:

services.kubernetes.roles = [ "master" ];

While this will enable the kubelet and kube-proxy only:

services.kubernetes.roles = [ "node" ];

Assigning both the master and node roles is usable if you want a single node Kubernetes cluster for dev or testing purposes:

services.kubernetes.roles = [ "master" "node" ];

Note: Assigning either role will also default both services.kubernetes.flannel.enable and services.kubernetes.easyCerts to true. This sets up flannel as CNI and activates automatic PKI bootstrapping.

As of kubernetes 1.10.X it has been deprecated to open non-tls-enabled ports on kubernetes components. Thus, from NixOS 19.03 all plain HTTP ports have been disabled by default. While opening insecure ports is still possible, it is recommended not to bind these to other interfaces than loopback. To re-enable the insecure port on the apiserver, see options: services.kubernetes.apiserver.insecurePort and services.kubernetes.apiserver.insecureBindAddress

Note: As of NixOS 19.03, it is mandatory to configure: services.kubernetes.masterAddress. The masterAddress must be resolveable and routeable by all cluster nodes. In single node clusters, this can be set to localhost.

Role-based access control (RBAC) authorization mode is enabled by default. This means that anonymous requests to the apiserver secure port will expectedly cause a permission denied error. All cluster components must therefore be configured with x509 certificates for two-way tls communication. The x509 certificate subject section determines the roles and permissions granted by the apiserver to perform clusterwide or namespaced operations. See also: Using RBAC Authorization.

The NixOS kubernetes module provides an option for automatic certificate bootstrapping and configuration, services.kubernetes.easyCerts. The PKI bootstrapping process involves setting up a certificate authority (CA) daemon (cfssl) on the kubernetes master node. cfssl generates a CA-cert for the cluster, and uses the CA-cert for signing subordinate certs issued to each of the cluster components. Subsequently, the certmgr daemon monitors active certificates and renews them when needed. For single node Kubernetes clusters, setting services.kubernetes.easyCerts = true is sufficient and no further action is required. For joining extra node machines to an existing cluster on the other hand, establishing initial trust is mandatory.

To add new nodes to the cluster: On any (non-master) cluster node where services.kubernetes.easyCerts is enabled, the helper script nixos-kubernetes-node-join is available on PATH. Given a token on stdin, it will copy the token to the kubernetes secrets directory and restart the certmgr service. As requested certificates are issued, the script will restart kubernetes cluster components as needed for them to pick up new keypairs.

Note: Multi-master (HA) clusters are not supported by the easyCerts module.

In order to interact with an RBAC-enabled cluster as an administrator, one needs to have cluster-admin privileges. By default, when easyCerts is enabled, a cluster-admin kubeconfig file is generated and linked into /etc/kubernetes/cluster-admin.kubeconfig as determined by services.kubernetes.pki.etcClusterAdminKubeconfig. export KUBECONFIG=/etc/kubernetes/cluster-admin.kubeconfig will make kubectl use this kubeconfig to access and authenticate the cluster. The cluster-admin kubeconfig references an auto-generated keypair owned by root. Thus, only root on the kubernetes master may obtain cluster-admin rights by means of this file.

This chapter describes various aspects of managing a running NixOS system, such as how to use the systemd service manager.

Chapter 35. Service Management

In NixOS, all system services are started and monitored using the systemd program. Systemd is the “init” process of the system (i.e. PID 1), the parent of all other processes. It manages a set of so-called “units”, which can be things like system services (programs), but also mount points, swap files, devices, targets (groups of units) and more. Units can have complex dependencies; for instance, one unit can require that another unit must be successfully started before the first unit can be started. When the system boots, it starts a unit named; the dependencies of this unit cause all system services to be started, file systems to be mounted, swap files to be activated, and so on.

The command systemctl is the main way to interact with systemd. Without any arguments, it shows the status of active units:

$ systemctl
-.mount          loaded active mounted   /
swapfile.swap    loaded active active    /swapfile
sshd.service     loaded active running   SSH Daemon loaded active active    Graphical Interface

You can ask for detailed status information about a unit, for instance, the PostgreSQL database service:

$ systemctl status postgresql.service
postgresql.service - PostgreSQL Server
          Loaded: loaded (/nix/store/pn3q73mvh75gsrl8w7fdlfk3fq5qm5mw-unit/postgresql.service)
          Active: active (running) since Mon, 2013-01-07 15:55:57 CET; 9h ago
        Main PID: 2390 (postgres)
          CGroup: name=systemd:/system/postgresql.service
                  ├─2390 postgres
                  ├─2418 postgres: writer process
                  ├─2419 postgres: wal writer process
                  ├─2420 postgres: autovacuum launcher process
                  ├─2421 postgres: stats collector process
                  └─2498 postgres: zabbix zabbix [local] idle

Jan 07 15:55:55 hagbard postgres[2394]: [1-1] LOG:  database system was shut down at 2013-01-07 15:55:05 CET
Jan 07 15:55:57 hagbard postgres[2390]: [1-1] LOG:  database system is ready to accept connections
Jan 07 15:55:57 hagbard postgres[2420]: [1-1] LOG:  autovacuum launcher started
Jan 07 15:55:57 hagbard systemd[1]: Started PostgreSQL Server.

Note that this shows the status of the unit (active and running), all the processes belonging to the service, as well as the most recent log messages from the service.

Units can be stopped, started or restarted:

# systemctl stop postgresql.service
# systemctl start postgresql.service
# systemctl restart postgresql.service

These operations are synchronous: they wait until the service has finished starting or stopping (or has failed). Starting a unit will cause the dependencies of that unit to be started as well (if necessary).

Chapter 36. Rebooting and Shutting Down

The system can be shut down (and automatically powered off) by doing:

# shutdown

This is equivalent to running systemctl poweroff.

To reboot the system, run

# reboot

which is equivalent to systemctl reboot. Alternatively, you can quickly reboot the system using kexec, which bypasses the BIOS by directly loading the new kernel into memory:

# systemctl kexec

The machine can be suspended to RAM (if supported) using systemctl suspend, and suspended to disk using systemctl hibernate.

These commands can be run by any user who is logged in locally, i.e. on a virtual console or in X11; otherwise, the user is asked for authentication.

Chapter 37. User Sessions

Systemd keeps track of all users who are logged into the system (e.g. on a virtual console or remotely via SSH). The command loginctl allows querying and manipulating user sessions. For instance, to list all user sessions:

$ loginctl
   SESSION        UID USER             SEAT
        c1        500 eelco            seat0
        c3          0 root             seat0
        c4        500 alice

This shows that two users are logged in locally, while another is logged in remotely. (“Seats” are essentially the combinations of displays and input devices attached to the system; usually, there is only one seat.) To get information about a session:

$ loginctl session-status c3
c3 - root (0)
           Since: Tue, 2013-01-08 01:17:56 CET; 4min 42s ago
          Leader: 2536 (login)
            Seat: seat0; vc3
             TTY: /dev/tty3
         Service: login; type tty; class user
           State: online
          CGroup: name=systemd:/user/root/c3
                  ├─ 2536 /nix/store/10mn4xip9n7y9bxqwnsx7xwx2v2g34xn-shadow- --
                  ├─10339 -bash
                  └─10355 w3m

This shows that the user is logged in on virtual console 3. It also lists the processes belonging to this session. Since systemd keeps track of this, you can terminate a session in a way that ensures that all the session’s processes are gone:

# loginctl terminate-session c3

Chapter 38. Control Groups

To keep track of the processes in a running system, systemd uses control groups (cgroups). A control group is a set of processes used to allocate resources such as CPU, memory or I/O bandwidth. There can be multiple control group hierarchies, allowing each kind of resource to be managed independently.

The command systemd-cgls lists all control groups in the systemd hierarchy, which is what systemd uses to keep track of the processes belonging to each service or user session:

$ systemd-cgls
│ └─eelco
│   └─c1
│     ├─ 2567 -:0
│     ├─ 2682 kdeinit4: kdeinit4 Running...
│     ├─ ...
│     └─10851 sh -c less -R
  │ ├─2444 httpd -f /nix/store/3pyacby5cpr55a03qwbnndizpciwq161-httpd.conf -DNO_DETACH
  │ └─...
  │ └─2376 dhcpcd --config /nix/store/f8dif8dsi2yaa70n03xir8r653776ka6-dhcpcd.conf
  └─ ...

Similarly, systemd-cgls cpu shows the cgroups in the CPU hierarchy, which allows per-cgroup CPU scheduling priorities. By default, every systemd service gets its own CPU cgroup, while all user sessions are in the top-level CPU cgroup. This ensures, for instance, that a thousand run-away processes in the httpd.service cgroup cannot starve the CPU for one process in the postgresql.service cgroup. (By contrast, it they were in the same cgroup, then the PostgreSQL process would get 1/1001 of the cgroup’s CPU time.) You can limit a service’s CPU share in configuration.nix: = 512;

By default, every cgroup has 1024 CPU shares, so this will halve the CPU allocation of the httpd.service cgroup.

There also is a memory hierarchy that controls memory allocation limits; by default, all processes are in the top-level cgroup, so any service or session can exhaust all available memory. Per-cgroup memory limits can be specified in configuration.nix; for instance, to limit httpd.service to 512 MiB of RAM (excluding swap): = "512M";

The command systemd-cgtop shows a continuously updated list of all cgroups with their CPU and memory usage.

Chapter 39. Logging

System-wide logging is provided by systemd’s journal, which subsumes traditional logging daemons such as syslogd and klogd. Log entries are kept in binary files in /var/log/journal/. The command journalctl allows you to see the contents of the journal. For example,

$ journalctl -b

shows all journal entries since the last reboot. (The output of journalctl is piped into less by default.) You can use various options and match operators to restrict output to messages of interest. For instance, to get all messages from PostgreSQL:

$ journalctl -u postgresql.service
-- Logs begin at Mon, 2013-01-07 13:28:01 CET, end at Tue, 2013-01-08 01:09:57 CET. --
Jan 07 15:44:14 hagbard postgres[2681]: [2-1] LOG:  database system is shut down
-- Reboot --
Jan 07 15:45:10 hagbard postgres[2532]: [1-1] LOG:  database system was shut down at 2013-01-07 15:44:14 CET
Jan 07 15:45:13 hagbard postgres[2500]: [1-1] LOG:  database system is ready to accept connections

Or to get all messages since the last reboot that have at least a “critical” severity level:

$ journalctl -b -p crit
Dec 17 21:08:06 mandark sudo[3673]: pam_unix(sudo:auth): auth could not identify password for [alice]
Dec 29 01:30:22 mandark kernel[6131]: [1053513.909444] CPU6: Core temperature above threshold, cpu clock throttled (total events = 1)

The system journal is readable by root and by users in the wheel and systemd-journal groups. All users have a private journal that can be read using journalctl.

Chapter 40. Cleaning the Nix Store

Table of Contents

40.1. NixOS Boot Entries

Nix has a purely functional model, meaning that packages are never upgraded in place. Instead new versions of packages end up in a different location in the Nix store (/nix/store). You should periodically run Nix’s garbage collector to remove old, unreferenced packages. This is easy:

$ nix-collect-garbage

Alternatively, you can use a systemd unit that does the same in the background:

# systemctl start nix-gc.service

You can tell NixOS in configuration.nix to run this unit automatically at certain points in time, for instance, every night at 03:15:

nix.gc.automatic = true;
nix.gc.dates = "03:15";

The commands above do not remove garbage collector roots, such as old system configurations. Thus they do not remove the ability to roll back to previous configurations. The following command deletes old roots, removing the ability to roll back to them:

$ nix-collect-garbage -d

You can also do this for specific profiles, e.g.

$ nix-env -p /nix/var/nix/profiles/per-user/eelco/profile --delete-generations old

Note that NixOS system configurations are stored in the profile /nix/var/nix/profiles/system.

Another way to reclaim disk space (often as much as 40% of the size of the Nix store) is to run Nix’s store optimiser, which seeks out identical files in the store and replaces them with hard links to a single copy.

$ nix-store --optimise

Since this command needs to read the entire Nix store, it can take quite a while to finish.

40.1. NixOS Boot Entries

If your /boot partition runs out of space, after clearing old profiles you must rebuild your system with nixos-rebuild to update the /boot partition and clear space.

Chapter 41. Container Management

NixOS allows you to easily run other NixOS instances as containers. Containers are a light-weight approach to virtualisation that runs software in the container at the same speed as in the host system. NixOS containers share the Nix store of the host, making container creation very efficient.

Warning: Currently, NixOS containers are not perfectly isolated from the host system. This means that a user with root access to the container can do things that affect the host. So you should not give container root access to untrusted users.

NixOS containers can be created in two ways: imperatively, using the command nixos-container, and declaratively, by specifying them in your configuration.nix. The declarative approach implies that containers get upgraded along with your host system when you run nixos-rebuild, which is often not what you want. By contrast, in the imperative approach, containers are configured and updated independently from the host system.

41.1. Imperative Container Management

We’ll cover imperative container management using nixos-container first. Be aware that container management is currently only possible as root.

You create a container with identifier foo as follows:

# nixos-container create foo

This creates the container’s root directory in /var/lib/containers/foo and a small configuration file in /etc/containers/foo.conf. It also builds the container’s initial system configuration and stores it in /nix/var/nix/profiles/per-container/foo/system. You can modify the initial configuration of the container on the command line. For instance, to create a container that has sshd running, with the given public key for root:

# nixos-container create foo --config '
  services.openssh.enable = true;
  users.users.root.openssh.authorizedKeys.keys = ["ssh-dss AAAAB3N…"];

By default the next free address in the subnet will be chosen as container IP. This behavior can be altered by setting --host-address and --local-address:

# nixos-container create test --config-file test-container.nix \
    --local-address --host-address

Creating a container does not start it. To start the container, run:

# nixos-container start foo

This command will return as soon as the container has booted and has reached On the host, the container runs within a systemd unit called container@container-name.service. Thus, if something went wrong, you can get status info using systemctl:

# systemctl status container@foo

If the container has started successfully, you can log in as root using the root-login operation:

# nixos-container root-login foo

Note that only root on the host can do this (since there is no authentication). You can also get a regular login prompt using the login operation, which is available to all users on the host:

# nixos-container login foo
foo login: alice
Password: ***

With nixos-container run, you can execute arbitrary commands in the container:

# nixos-container run foo -- uname -a
Linux foo 3.4.82 #1-NixOS SMP Thu Mar 20 14:44:05 UTC 2014 x86_64 GNU/Linux

There are several ways to change the configuration of the container. First, on the host, you can edit /var/lib/container/name/etc/nixos/configuration.nix, and run

# nixos-container update foo

This will build and activate the new configuration. You can also specify a new configuration on the command line:

# nixos-container update foo --config '
  services.httpd.enable = true;
  services.httpd.adminAddr = "";
  networking.firewall.allowedTCPPorts = [ 80 ];

# curl http://$(nixos-container show-ip foo)/

However, note that this will overwrite the container’s /etc/nixos/configuration.nix.

Alternatively, you can change the configuration from within the container itself by running nixos-rebuild switch inside the container. Note that the container by default does not have a copy of the NixOS channel, so you should run nix-channel --update first.

Containers can be stopped and started using nixos-container stop and nixos-container start, respectively, or by using systemctl on the container’s service unit. To destroy a container, including its file system, do

# nixos-container destroy foo

41.2. Declarative Container Specification

You can also specify containers and their configuration in the host’s configuration.nix. For example, the following specifies that there shall be a container named database running PostgreSQL:

containers.database =
  { config =
      { config, pkgs, ... }:
      { services.postgresql.enable = true;
      services.postgresql.package = pkgs.postgresql_9_6;

If you run nixos-rebuild switch, the container will be built. If the container was already running, it will be updated in place, without rebooting. The container can be configured to start automatically by setting containers.database.autoStart = true in its configuration.

By default, declarative containers share the network namespace of the host, meaning that they can listen on (privileged) ports. However, they cannot change the network configuration. You can give a container its own network as follows:

containers.database = {
  privateNetwork = true;
  hostAddress = "";
  localAddress = "";

This gives the container a private virtual Ethernet interface with IP address, which is hooked up to a virtual Ethernet interface on the host with IP address (See the next section for details on container networking.)

To disable the container, just remove it from configuration.nix and run nixos-rebuild switch. Note that this will not delete the root directory of the container in /var/lib/containers. Containers can be destroyed using the imperative method: nixos-container destroy foo.

Declarative containers can be started and stopped using the corresponding systemd service, e.g. systemctl start container@database.

41.3. Container Networking

When you create a container using nixos-container create, it gets it own private IPv4 address in the range You can get the container’s IPv4 address as follows:

# nixos-container show-ip foo

$ ping -c1
64 bytes from icmp_seq=1 ttl=64 time=0.106 ms

Networking is implemented using a pair of virtual Ethernet devices. The network interface in the container is called eth0, while the matching interface in the host is called ve-container-name (e.g., ve-foo). The container has its own network namespace and the CAP_NET_ADMIN capability, so it can perform arbitrary network configuration such as setting up firewall rules, without affecting or having access to the host’s network.

By default, containers cannot talk to the outside network. If you want that, you should set up Network Address Translation (NAT) rules on the host to rewrite container traffic to use your external IP address. This can be accomplished using the following configuration on the host:

networking.nat.enable = true;
networking.nat.internalInterfaces = ["ve-+"];
networking.nat.externalInterface = "eth0";

where eth0 should be replaced with the desired external interface. Note that ve-+ is a wildcard that matches all container interfaces.

If you are using Network Manager, you need to explicitly prevent it from managing container interfaces:

networking.networkmanager.unmanaged = [ "interface-name:ve-*" ];

You may need to restart your system for the changes to take effect.

Chapter 42. Troubleshooting

This chapter describes solutions to common problems you might encounter when you manage your NixOS system.

42.1. Boot Problems

If NixOS fails to boot, there are a number of kernel command line parameters that may help you to identify or fix the issue. You can add these parameters in the GRUB boot menu by pressing “e” to modify the selected boot entry and editing the line starting with linux. The following are some useful kernel command line parameters that are recognised by the NixOS boot scripts or by systemd:


Start a root shell if something goes wrong in stage 1 of the boot process (the initial ramdisk). This is disabled by default because there is no authentication for the root shell.


Start an interactive shell in stage 1 before anything useful has been done. That is, no modules have been loaded and no file systems have been mounted, except for /proc and /sys.


Print every shell command executed by the stage 1 and 2 boot scripts.


Boot into rescue mode (a.k.a. single user mode). This will cause systemd to start nothing but the unit, which runs sulogin to prompt for the root password and start a root login shell. Exiting the shell causes the system to continue with the normal boot process.

systemd.log_level=debug systemd.log_target=console

Make systemd very verbose and send log messages to the console instead of the journal.

For more parameters recognised by systemd, see systemd(1).

If no login prompts or X11 login screens appear (e.g. due to hanging dependencies), you can press Alt+ArrowUp. If you’re lucky, this will start rescue mode (described above). (Also note that since most units have a 90-second timeout before systemd gives up on them, the agetty login prompts should appear eventually unless something is very wrong.)

42.2. Maintenance Mode

You can enter rescue mode by running:

# systemctl rescue

This will eventually give you a single-user root shell. Systemd will stop (almost) all system services. To get out of maintenance mode, just exit from the rescue shell.

42.3. Rolling Back Configuration Changes

After running nixos-rebuild to switch to a new configuration, you may find that the new configuration doesn’t work very well. In that case, there are several ways to return to a previous configuration.

First, the GRUB boot manager allows you to boot into any previous configuration that hasn’t been garbage-collected. These configurations can be found under the GRUB submenu “NixOS - All configurations”. This is especially useful if the new configuration fails to boot. After the system has booted, you can make the selected configuration the default for subsequent boots:

# /run/current-system/bin/switch-to-configuration boot

Second, you can switch to the previous configuration in a running system:

# nixos-rebuild switch --rollback

This is equivalent to running:

# /nix/var/nix/profiles/system-N-link/bin/switch-to-configuration switch

where N is the number of the NixOS system configuration. To get a list of the available configurations, do:

$ ls -l /nix/var/nix/profiles/system-*-link
lrwxrwxrwx 1 root root 78 Aug 12 13:54 /nix/var/nix/profiles/system-268-link -> /nix/store/202b...-nixos-13.07pre4932_5a676e4-4be1055

42.4. Nix Store Corruption

After a system crash, it’s possible for files in the Nix store to become corrupted. (For instance, the Ext4 file system has the tendency to replace un-synced files with zero bytes.) NixOS tries hard to prevent this from happening: it performs a sync before switching to a new configuration, and Nix’s database is fully transactional. If corruption still occurs, you may be able to fix it automatically.

If the corruption is in a path in the closure of the NixOS system configuration, you can fix it by doing

# nixos-rebuild switch --repair

This will cause Nix to check every path in the closure, and if its cryptographic hash differs from the hash recorded in Nix’s database, the path is rebuilt or redownloaded.

You can also scan the entire Nix store for corrupt paths:

# nix-store --verify --check-contents --repair

Any corrupt paths will be redownloaded if they’re available in a binary cache; otherwise, they cannot be repaired.

42.5. Network Problems

Nix uses a so-called binary cache to optimise building a package from source into downloading it as a pre-built binary. That is, whenever a command like nixos-rebuild needs a path in the Nix store, Nix will try to download that path from the Internet rather than build it from source. The default binary cache is If this cache is unreachable, Nix operations may take a long time due to HTTP connection timeouts. You can disable the use of the binary cache by adding --option use-binary-caches false, e.g.

# nixos-rebuild switch --option use-binary-caches false

If you have an alternative binary cache at your disposal, you can use it instead:

# nixos-rebuild switch --option binary-caches

Chapter 43. Getting the Sources

By default, NixOS’s nixos-rebuild command uses the NixOS and Nixpkgs sources provided by the nixos channel (kept in /nix/var/nix/profiles/per-user/root/channels/nixos). To modify NixOS, however, you should check out the latest sources from Git. This is as follows:

$ git clone
$ cd nixpkgs
$ git remote update origin

This will check out the latest Nixpkgs sources to ./nixpkgs the NixOS sources to ./nixpkgs/nixos. (The NixOS source tree lives in a subdirectory of the Nixpkgs repository.) The nixpkgs repository has branches that correspond to each Nixpkgs/NixOS channel (see Chapter 4, Upgrading NixOS for more information about channels). Thus, the Git branch origin/nixos-17.03 will contain the latest built and tested version available in the nixos-17.03 channel.

It’s often inconvenient to develop directly on the master branch, since if somebody has just committed (say) a change to GCC, then the binary cache may not have caught up yet and you’ll have to rebuild everything from source. So you may want to create a local branch based on your current NixOS version:

$ nixos-version
17.09pre104379.6e0b727 (Hummingbird)

$ git checkout -b local 6e0b727

Or, to base your local branch on the latest version available in a NixOS channel:

$ git remote update origin
$ git checkout -b local origin/nixos-17.03

(Replace nixos-17.03 with the name of the channel you want to use.) You can use git merge or git rebase to keep your local branch in sync with the channel, e.g.

$ git remote update origin
$ git merge origin/nixos-17.03

You can use git cherry-pick to copy commits from your local branch to the upstream branch.

If you want to rebuild your system using your (modified) sources, you need to tell nixos-rebuild about them using the -I flag:

# nixos-rebuild switch -I nixpkgs=/my/sources/nixpkgs

If you want nix-env to use the expressions in /my/sources, use nix-env -f /my/sources/nixpkgs, or change the default by adding a symlink in ~/.nix-defexpr:

$ ln -s /my/sources/nixpkgs ~/.nix-defexpr/nixpkgs

You may want to delete the symlink ~/.nix-defexpr/channels_root to prevent root’s NixOS channel from clashing with your own tree (this may break the command-not-found utility though). If you want to go back to the default state, you may just remove the ~/.nix-defexpr directory completely, log out and log in again and it should have been recreated with a link to the root channels.

Chapter 44. Writing NixOS Modules

NixOS has a modular system for declarative configuration. This system combines multiple modules to produce the full system configuration. One of the modules that constitute the configuration is /etc/nixos/configuration.nix. Most of the others live in the nixos/modules subdirectory of the Nixpkgs tree.

Each NixOS module is a file that handles one logical aspect of the configuration, such as a specific kind of hardware, a service, or network settings. A module configuration does not have to handle everything from scratch; it can use the functionality provided by other modules for its implementation. Thus a module can declare options that can be used by other modules, and conversely can define options provided by other modules in its own implementation. For example, the module pam.nix declares the option that allows other modules (e.g. sshd.nix) to define PAM services; and it defines the option environment.etc (declared by etc.nix) to cause files to be created in /etc/pam.d.

In Chapter 5, Configuration Syntax, we saw the following structure of NixOS modules:

{ config, pkgs, ... }:

{ option definitions

This is actually an abbreviated form of module that only defines options, but does not declare any. The structure of full NixOS modules is shown in Example 44.1, “Structure of NixOS Modules”.

Example 44.1. Structure of NixOS Modules

{ config, pkgs, ... }: 1

  imports =
    [ paths of other modules 2

  options = {
    option declarations 3

  config = {
    option definitions 4

The meaning of each part is as follows.


This line makes the current Nix expression a function. The variable pkgs contains Nixpkgs, while config contains the full system configuration. This line can be omitted if there is no reference to pkgs and config inside the module.


This list enumerates the paths to other NixOS modules that should be included in the evaluation of the system configuration. A default set of modules is defined in the file modules/module-list.nix. These don't need to be added in the import list.


The attribute options is a nested set of option declarations (described below).


The attribute config is a nested set of option definitions (also described below).

Example 44.2, “NixOS Module for the “locate” Service” shows a module that handles the regular update of the “locate” database, an index of all files in the file system. This module declares two options that can be defined by other modules (typically the user’s configuration.nix): services.locate.enable (whether the database should be updated) and services.locate.interval (when the update should be done). It implements its functionality by defining two options declared by other modules: (the set of all systemd services) and systemd.timers (the list of commands to be executed periodically by systemd).

Example 44.2. NixOS Module for the “locate” Service

{ config, lib, pkgs, ... }:

with lib;

  cfg =;
in { = {
    enable = mkOption {
      type = types.bool;
      default = false;
      description = ''
        If enabled, NixOS will periodically update the database of
        files used by the locate command.

    interval = mkOption {
      type = types.str;
      default = "02:15";
      example = "hourly";
      description = ''
        Update the locate database at this interval. Updates by
        default at 2:15 AM every day.

        The format is described in

    # Other options omitted for documentation

  config = { =
      { description = "Update Locate Database";
        path  = [ ];
        script =
            mkdir -m 0755 -p $(dirname ${toString cfg.output})
            exec updatedb \
              --localuser=${cfg.localuser} \
              ${optionalString (!cfg.includeStore) "--prunepaths='/nix/store'"} \
              --output=${toString cfg.output} ${concatStringsSep " " cfg.extraFlags}

    systemd.timers.update-locatedb = mkIf cfg.enable
      { description = "Update timer for locate database";
        partOf      = [ "update-locatedb.service" ];
        wantedBy    = [ "" ];
        timerConfig.OnCalendar = cfg.interval;

44.1. Option Declarations

An option declaration specifies the name, type and description of a NixOS configuration option. It is invalid to define an option that hasn’t been declared in any module. An option declaration generally looks like this:

options = {
  name = mkOption {
    type = type specification;
    default = default value;
    example = example value;
    description = "Description for use in the NixOS manual.";

The attribute names within the name attribute path must be camel cased in general but should, as an exception, match the package attribute name when referencing a Nixpkgs package. For example, the option services.nix-serve.bindAddress references the nix-serve Nixpkgs package.

The function mkOption accepts the following arguments.


The type of the option (see Section 44.2, “Options Types”). It may be omitted, but that’s not advisable since it may lead to errors that are hard to diagnose.


The default value used if no value is defined by any module. A default is not required; but if a default is not given, then users of the module will have to define the value of the option, otherwise an error will be thrown.


An example value that will be shown in the NixOS manual.


A textual description of the option, in DocBook format, that will be included in the NixOS manual.

44.1.1. Extensible Option Types

Extensible option types is a feature that allow to extend certain types declaration through multiple module files. This feature only work with a restricted set of types, namely enum and submodules and any composed forms of them.

Extensible option types can be used for enum options that affects multiple modules, or as an alternative to related enable options.

As an example, we will take the case of display managers. There is a central display manager module for generic display manager options and a module file per display manager backend (sddm, gdm ...).

There are two approach to this module structure:

  • Managing the display managers independently by adding an enable option to every display manager module backend. (NixOS)

  • Managing the display managers in the central module by adding an option to select which display manager backend to use.

Both approaches have problems.

Making backends independent can quickly become hard to manage. For display managers, there can be only one enabled at a time, but the type system can not enforce this restriction as there is no relation between each backend enable option. As a result, this restriction has to be done explicitely by adding assertions in each display manager backend module.

On the other hand, managing the display managers backends in the central module will require to change the central module option every time a new backend is added or removed.

By using extensible option types, it is possible to create a placeholder option in the central module (Example 44.3, “Extensible type placeholder in the service module”), and to extend it in each backend module (Example 44.4, “Extending services.xserver.displayManager.enable in the gdm module”, Example 44.5, “Extending services.xserver.displayManager.enable in the sddm module”).

As a result, displayManager.enable option values can be added without changing the main service module file and the type system automatically enforce that there can only be a single display manager enabled.

Example 44.3. Extensible type placeholder in the service module

services.xserver.displayManager.enable = mkOption {
  description = "Display manager to use";
  type = with types; nullOr (enum [ ]);

Example 44.4. Extending services.xserver.displayManager.enable in the gdm module

services.xserver.displayManager.enable = mkOption {
  type = with types; nullOr (enum [ "gdm" ]);

Example 44.5. Extending services.xserver.displayManager.enable in the sddm module

services.xserver.displayManager.enable = mkOption {
  type = with types; nullOr (enum [ "sddm" ]);

The placeholder declaration is a standard mkOption declaration, but it is important that extensible option declarations only use the type argument.

Extensible option types work with any of the composed variants of enum such as with types; nullOr (enum [ "foo" "bar" ]) or with types; listOf (enum [ "foo" "bar" ]).

44.2. Options Types

Option types are a way to put constraints on the values a module option can take. Types are also responsible of how values are merged in case of multiple value definitions.

44.2.1. Basic Types

Basic types are the simplest available types in the module system. Basic types include multiple string types that mainly differ in how definition merging is handled.


A free-form attribute set.


A boolean, its values can be true or false.


A filesystem path, defined as anything that when coerced to a string starts with a slash. Even if derivations can be considered as path, the more specific types.package should be preferred.


A derivation or a store path.

Integer-related types:

A signed integer.

types.ints.{s8, s16, s32}

Signed integers with a fixed length (8, 16 or 32 bits). They go from −2n/2 to 2n/2−1 respectively (e.g. −128 to 127 for 8 bits).


An unsigned integer (that is >= 0).

types.ints.{u8, u16, u32}

Unsigned integers with a fixed length (8, 16 or 32 bits). They go from 0 to 2n−1 respectively (e.g. 0 to 255 for 8 bits).


A positive integer (that is > 0).


A port number. This type is an alias to types.ints.u16.

String-related types:


A string. Multiple definitions cannot be merged.


A string. Multiple definitions are concatenated with a new line "\n".


A string. Multiple definitions are concatenated with a comma ",".


A string. Multiple definitions are concatenated with a collon ":".


A string matching a specific regular expression. Multiple definitions cannot be merged. The regular expression is processed using builtins.match.

44.2.2. Value Types

Value types are types that take a value parameter.

types.enum l

One element of the list l, e.g. types.enum [ "left" "right" ]. Multiple definitions cannot be merged.

types.separatedString sep

A string with a custom separator sep, e.g. types.separatedString "|".

types.ints.between lowest highest

An integer between lowest and highest (both inclusive). Useful for creating types like types.port.

types.submodule o

A set of sub options o. o can be an attribute set, a function returning an attribute set, or a path to a file containing such a value. Submodules are used in composed types to create modular options. This is equivalent to types.submoduleWith { modules = toList o; shorthandOnlyDefinesConfig = true; }. Submodules are detailed in Section 44.2.4, “Submodule”.

types.submoduleWith { modules, specialArgs ? {}, shorthandOnlyDefinesConfig ? false }

Like types.submodule, but more flexible and with better defaults. It has parameters

  • modules A list of modules to use by default for this submodule type. This gets combined with all option definitions to build the final list of modules that will be included.

    Note: Only options defined with this argument are included in rendered documentation.

  • specialArgs An attribute set of extra arguments to be passed to the module functions. The option _module.args should be used instead for most arguments since it allows overriding. specialArgs should only be used for arguments that can't go through the module fixed-point, because of infinite recursion or other problems. An example is overriding the lib argument, because lib itself is used to define _module.args, which makes using _module.args to define it impossible.

  • shorthandOnlyDefinesConfig Whether definitions of this type should default to the config section of a module (see Example 44.1, “Structure of NixOS Modules”) if it is an attribute set. Enabling this only has a benefit when the submodule defines an option named config or options. In such a case it would allow the option to be set with the-submodule.config = "value" instead of requiring the-submodule.config.config = "value". This is because only when modules don't set the config or options keys, all keys are interpreted as option definitions in the config section. Enabling this option implicitly puts all attributes in the config section.

    With this option enabled, defining a non-config section requires using a function: the-submodule = { ... }: { options = { ... }; }.

44.2.3. Composed Types

Composed types are types that take a type as parameter. listOf int and either int str are examples of composed types.

types.listOf t

A list of t type, e.g. types.listOf int. Multiple definitions are merged with list concatenation.

types.attrsOf t

An attribute set of where all the values are of t type. Multiple definitions result in the joined attribute set.

Note: This type is strict in its values, which in turn means attributes cannot depend on other attributes. See types.lazyAttrsOf for a lazy version.

types.lazyAttrsOf t

An attribute set of where all the values are of t type. Multiple definitions result in the joined attribute set. This is the lazy version of types.attrsOf , allowing attributes to depend on each other.

Warning: This version does not fully support conditional definitions! With an option foo of this type and a definition foo.attr = lib.mkIf false 10, evaluating foo ? attr will return true even though it should be false. Accessing the value will then throw an error. For types t that have an emptyValue defined, that value will be returned instead of throwing an error. So if the type of foo.attr was lazyAttrsOf (nullOr int), null would be returned instead for the same mkIf false definition.

types.loaOf t

An attribute set or a list of t type. Multiple definitions are merged according to the value.

types.nullOr t

null or type t. Multiple definitions are merged according to type t.

types.uniq t

Ensures that type t cannot be merged. It is used to ensure option definitions are declared only once.

types.either t1 t2

Type t1 or type t2, e.g. with types; either int str. Multiple definitions cannot be merged.

types.oneOf [ t1 t2 ... ]

Type t1 or type t2 and so forth, e.g. with types; oneOf [ int str bool ]. Multiple definitions cannot be merged.

types.coercedTo from f to

Type to or type from which will be coerced to type to using function f which takes an argument of type from and return a value of type to. Can be used to preserve backwards compatibility of an option if its type was changed.

44.2.4. Submodule

submodule is a very powerful type that defines a set of sub-options that are handled like a separate module.

It takes a parameter o, that should be a set, or a function returning a set with an options key defining the sub-options. Submodule option definitions are type-checked accordingly to the options declarations. Of course, you can nest submodule option definitons for even higher modularity.

The option set can be defined directly (Example 44.6, “Directly defined submodule”) or as reference (Example 44.7, “Submodule defined as a reference”).

Example 44.6. Directly defined submodule

options.mod = mkOption {
  description = "submodule example";
  type = with types; submodule {
    options = {
      foo = mkOption {
        type = int;
      bar = mkOption {
        type = str;

Example 44.7. Submodule defined as a reference

  modOptions = {
    options = {
      foo = mkOption {
        type = int;
      bar = mkOption {
        type = int;
options.mod = mkOption {
  description = "submodule example";
  type = with types; submodule modOptions;

The submodule type is especially interesting when used with composed types like attrsOf or listOf. When composed with listOf (Example 44.8, “Declaration of a list of submodules”), submodule allows multiple definitions of the submodule option set (Example 44.9, “Definition of a list of submodules”).

Example 44.8. Declaration of a list of submodules

options.mod = mkOption {
  description = "submodule example";
  type = with types; listOf (submodule {
    options = {
      foo = mkOption {
        type = int;
      bar = mkOption {
        type = str;

Example 44.9. Definition of a list of submodules

config.mod = [
  { foo = 1; bar = "one"; }
  { foo = 2; bar = "two"; }

When composed with attrsOf (Example 44.10, “Declaration of attribute sets of submodules”), submodule allows multiple named definitions of the submodule option set (Example 44.11, “Declaration of attribute sets of submodules”).

Example 44.10. Declaration of attribute sets of submodules

options.mod = mkOption {
  description = "submodule example";
  type = with types; attrsOf (submodule {
    options = {
      foo = mkOption {
        type = int;
      bar = mkOption {
        type = str;

Example 44.11. Declaration of attribute sets of submodules = { foo = 1; bar = "one"; };
config.mod.two = { foo = 2; bar = "two"; };

44.2.5. Extending types

Types are mainly characterized by their check and merge functions.


The function to type check the value. Takes a value as parameter and return a boolean. It is possible to extend a type check with the addCheck function (Example 44.12, “Adding a type check”), or to fully override the check function (Example 44.13, “Overriding a type check”).

Example 44.12. Adding a type check

byte = mkOption {
  description = "An integer between 0 and 255.";
  type = types.addCheck (x: x >= 0 && x <= 255);

Example 44.13. Overriding a type check

nixThings = mkOption {
  description = "words that start with 'nix'";
  type = types.str // {
    check = (x: lib.hasPrefix "nix" x)


Function to merge the options values when multiple values are set. The function takes two parameters, loc the option path as a list of strings, and defs the list of defined values as a list. It is possible to override a type merge function for custom needs.

44.2.6. Custom Types

Custom types can be created with the mkOptionType function. As type creation includes some more complex topics such as submodule handling, it is recommended to get familiar with types.nix code before creating a new type.

The only required parameter is name.


A string representation of the type function name.


Description of the type used in documentation. Give information of the type and any of its arguments.


A function to type check the definition value. Takes the definition value as a parameter and returns a boolean indicating the type check result, true for success and false for failure.


A function to merge multiple definitions values. Takes two parameters:


The option path as a list of strings, e.g. ["boot" "loader "grub" "enable"].


The list of sets of defined value and file where the value was defined, e.g. [ { file = "/foo.nix"; value = 1; } { file = "/bar.nix"; value = 2 } ]. The merge function should return the merged value or throw an error in case the values are impossible or not meant to be merged.


For composed types that can take a submodule as type parameter, this function generate sub-options documentation. It takes the current option prefix as a list and return the set of sub-options. Usually defined in a recursive manner by adding a term to the prefix, e.g. prefix: elemType.getSubOptions (prefix ++ ["prefix"]) where "prefix" is the newly added prefix.


For composed types that can take a submodule as type parameter, this function should return the type parameters submodules. If the type parameter is called elemType, the function should just recursively look into submodules by returning elemType.getSubModules;.


For composed types that can take a submodule as type parameter, this function can be used to substitute the parameter of a submodule type. It takes a module as parameter and return the type with the submodule options substituted. It is usually defined as a type function call with a recursive call to substSubModules, e.g for a type composedType that take an elemtype type parameter, this function should be defined as m: composedType (elemType.substSubModules m).


A function to merge multiple type declarations. Takes the type to merge functor as parameter. A null return value means that type cannot be merged.


The type to merge functor.

Note: There is a generic defaultTypeMerge that work with most of value and composed types.


An attribute set representing the type. It is used for type operations and has the following keys:


The type function.


Holds the type parameter for composed types.


Holds the value parameter for value types. The types that have a payload are the enum, separatedString and submodule types.


A binary operation that can merge the payloads of two same types. Defined as a function that take two payloads as parameters and return the payloads merged.

44.3. Option Definitions

Option definitions are generally straight-forward bindings of values to option names, like

config = {
  services.httpd.enable = true;

However, sometimes you need to wrap an option definition or set of option definitions in a property to achieve certain effects:

Delaying Conditionals

If a set of option definitions is conditional on the value of another option, you may need to use mkIf. Consider, for instance:

config = if then {
  environment.systemPackages = [ ... ];
} else {};

This definition will cause Nix to fail with an “infinite recursion” error. Why? Because the value of depends on the value being constructed here. After all, you could also write the clearly circular and contradictory:

config = if then {
  services.httpd.enable = false;
} else {
  services.httpd.enable = true;

The solution is to write:

config = mkIf {
  environment.systemPackages = [ ... ];

The special function mkIf causes the evaluation of the conditional to be “pushed down” into the individual definitions, as if you had written:

config = {
  environment.systemPackages = if then [ ... ] else [];

Setting Priorities

A module can override the definitions of an option in other modules by setting a priority. All option definitions that do not have the lowest priority value are discarded. By default, option definitions have priority 1000. You can specify an explicit priority by using mkOverride, e.g.

services.openssh.enable = mkOverride 10 false;

This definition causes all other definitions with priorities above 10 to be discarded. The function mkForce is equal to mkOverride 50.

Merging Configurations

In conjunction with mkIf, it is sometimes useful for a module to return multiple sets of option definitions, to be merged together as if they were declared in separate modules. This can be done using mkMerge:

config = mkMerge
  [ # Unconditional stuff.
    { environment.systemPackages = [ ... ];
    # Conditional stuff.
    (mkIf {
      environment.systemPackages = [ ... ];

44.4. Warnings and Assertions

When configuration problems are detectable in a module, it is a good idea to write an assertion or warning. Doing so provides clear feedback to the user and prevents errors after the build.

Although Nix has the abort and builtins.trace functions to perform such tasks, they are not ideally suited for NixOS modules. Instead of these functions, you can declare your warnings and assertions using the NixOS module system.

44.4.1. Warnings

This is an example of using warnings.

{ config, lib, ... }:
  config = lib.mkIf {
    warnings =
      then [ ''You have enabled the bar feature of the foo service.
               This is known to cause some specific problems in certain situations.
               '' ]
      else [];

44.4.2. Assertions

This example, extracted from the syslogd module shows how to use assertions. Since there can only be one active syslog daemon at a time, an assertion is useful to prevent such a broken system from being built.

{ config, lib, ... }:
  config = lib.mkIf {
    assertions =
      [ { assertion = !;
          message = "rsyslogd conflicts with syslogd";

44.5. Meta Attributes

Like Nix packages, NixOS modules can declare meta-attributes to provide extra information. Module meta attributes are defined in the meta.nix special module.

meta is a top level attribute like options and config. Available meta-attributes are maintainers and doc.

Each of the meta-attributes must be defined at most once per module file.

{ config, lib, pkgs, ... }:
  options = {

  config = {

  meta = {
    maintainers = with lib.maintainers; [ ericsagnes ]; 1
    doc = ./default.xml; 2


maintainers contains a list of the module maintainers.


doc points to a valid DocBook file containing the module documentation. Its contents is automatically added to Part II, “Configuration”. Changes to a module documentation have to be checked to not break building the NixOS manual:

$ nix-build nixos/release.nix -A manual

44.6. Importing Modules

Sometimes NixOS modules need to be used in configuration but exist outside of Nixpkgs. These modules can be imported:

{ config, lib, pkgs, ... }:

  imports =
    [ # Use a locally-available module definition in
      # ./example-module/default.nix

  services.exampleModule.enable = true;

The environment variable NIXOS_EXTRA_MODULE_PATH is an absolute path to a NixOS module that is included alongside the Nixpkgs NixOS modules. Like any NixOS module, this module can import additional modules:

# ./module-list/default.nix
# ./extra-module/default.nix
{ imports = import ./module-list.nix; }
# NIXOS_EXTRA_MODULE_PATH=/absolute/path/to/extra-module
{ config, lib, pkgs, ... }:

  # No `imports` needed

  services.exampleModule1.enable = true;

44.7. Replace Modules

Modules that are imported can also be disabled. The option declarations, config implementation and the imports of a disabled module will be ignored, allowing another to take it's place. This can be used to import a set of modules from another channel while keeping the rest of the system on a stable release.

disabledModules is a top level attribute like imports, options and config. It contains a list of modules that will be disabled. This can either be the full path to the module or a string with the filename relative to the modules path (eg. <nixpkgs/nixos/modules> for nixos).

This example will replace the existing postgresql module with the version defined in the nixos-unstable channel while keeping the rest of the modules and packages from the original nixos channel. This only overrides the module definition, this won't use postgresql from nixos-unstable unless explicitly configured to do so.

{ config, lib, pkgs, ... }:

  disabledModules = [ "services/databases/postgresql.nix" ];

  imports =
    [ # Use postgresql service from nixos-unstable channel.
      # sudo nix-channel --add nixos-unstable

  services.postgresql.enable = true;

This example shows how to define a custom module as a replacement for an existing module. Importing this module will disable the original module without having to know it's implementation details.

{ config, lib, pkgs, ... }:

with lib;

  cfg =;

  disabledModules = [ "services/programs/man.nix" ];

  options = { = mkOption {
      type = types.bool;
      default = true;
      description = "Whether to enable manual pages.";

  config = mkIf cfg.enabled {
    warnings = [ "disabled manpages for production deployments." ];

Chapter 45. Building Specific Parts of NixOS

With the command nix-build, you can build specific parts of your NixOS configuration. This is done as follows:

$ cd /path/to/nixpkgs/nixos
$ nix-build -A config.option

where option is a NixOS option with type “derivation” (i.e. something that can be built). Attributes of interest include:

The top-level option that builds the entire NixOS system. Everything else in your configuration is indirectly pulled in by this option. This is what nixos-rebuild builds and what /run/current-system points to afterwards.

A shortcut to build this is:

$ nix-build -A system

The NixOS manual.

A tree of symlinks that form the static parts of /etc. ,

The initial ramdisk and kernel of the system. This allows a quick way to test whether the kernel and the initial ramdisk boot correctly, by using QEMU’s -kernel and -initrd options:

$ nix-build -A -o initrd
$ nix-build -A -o kernel
$ qemu-system-x86_64 -kernel ./kernel/bzImage -initrd ./initrd/initrd -hda /dev/null , ,

These build the corresponding NixOS commands.


This builds the unit with the specified name. Note that since unit names contain dots (e.g. httpd.service), you need to put them between quotes, like this:

$ nix-build -A 'config.systemd.units."httpd.service".unit'

You can also test individual units, without rebuilding the whole system, by putting them in /run/systemd/system:

$ cp $(nix-build -A 'config.systemd.units."httpd.service".unit')/httpd.service \
# systemctl daemon-reload
# systemctl start tmp-httpd.service

Note that the unit must not have the same name as any unit in /etc/systemd/system since those take precedence over /run/systemd/system. That’s why the unit is installed as tmp-httpd.service here.

Chapter 46. Writing NixOS Documentation

As NixOS grows, so too does the need for a catalogue and explanation of its extensive functionality. Collecting pertinent information from disparate sources and presenting it in an accessible style would be a worthy contribution to the project.

46.1. Building the Manual

The DocBook sources of the NixOS Manual are in the nixos/doc/manual subdirectory of the Nixpkgs repository.

You can quickly validate your edits with make:

  $ cd /path/to/nixpkgs/nixos/doc/manual
  $ make

Once you are done making modifications to the manual, it's important to build it before committing. You can do that as follows:

nix-build nixos/release.nix -A manual.x86_64-linux

When this command successfully finishes, it will tell you where the manual got generated. The HTML will be accessible through the result symlink at ./result/share/doc/nixos/index.html.

46.2. Editing DocBook XML

For general information on how to write in DocBook, see DocBook 5: The Definitive Guide.

Emacs nXML Mode is very helpful for editing DocBook XML because it validates the document as you write, and precisely locates errors. To use it, see Section 23.3.3, “Editing DocBook 5 XML Documents”.

Pandoc can generate DocBook XML from a multitude of formats, which makes a good starting point.

Example 46.1. Pandoc invocation to convert GitHub-Flavoured MarkDown to DocBook 5 XML

pandoc -f markdown_github -t docbook5 -o

Pandoc can also quickly convert a single section.xml to HTML, which is helpful when drafting.

Sometimes writing valid DocBook is simply too difficult. In this case, submit your documentation updates in a GitHub Issue and someone will handle the conversion to XML for you.

46.3. Creating a Topic

You can use an existing topic as a basis for the new topic or create a topic from scratch.

Keep the following guidelines in mind when you create and add a topic:

  • The NixOS book element is in nixos/doc/manual/manual.xml. It includes several parts which are in subdirectories.

  • Store the topic file in the same directory as the part to which it belongs. If your topic is about configuring a NixOS module, then the XML file can be stored alongside the module definition nix file.

  • If you include multiple words in the file name, separate the words with a dash. For example: ipv6-config.xml.

  • Make sure that the xml:id value is unique. You can use abbreviations if the ID is too long. For example: nixos-config.

  • Determine whether your topic is a chapter or a section. If you are unsure, open an existing topic file and check whether the main element is chapter or section.

46.4. Adding a Topic to the Book

Open the parent XML file and add an xi:include element to the list of chapters with the file name of the topic that you created. If you created a section, you add the file to the chapter file. If you created a chapter, you add the file to the part file.

If the topic is about configuring a NixOS module, it can be automatically included in the manual by using the meta.doc attribute. See Section 44.5, “Meta Attributes” for an explanation.

Chapter 47. Building Your Own NixOS CD

Building a NixOS CD is as easy as configuring your own computer. The idea is to use another module which will replace your configuration.nix to configure the system that would be installed on the CD.

Default CD/DVD configurations are available inside nixos/modules/installer/cd-dvd.

$ git clone
$ cd nixpkgs/nixos
$ nix-build -A -I nixos-config=modules/installer/cd-dvd/installation-cd-minimal.nix default.nix

Before burning your CD/DVD, you can check the content of the image by mounting anywhere like suggested by the following command:

# mount -o loop -t iso9660 ./result/iso/cd.iso /mnt/iso

Chapter 48. NixOS Tests

When you add some feature to NixOS, you should write a test for it. NixOS tests are kept in the directory nixos/tests, and are executed (using Nix) by a testing framework that automatically starts one or more virtual machines containing the NixOS system(s) required for the test.

48.1. Writing Tests

A NixOS test is a Nix expression that has the following structure:

import ./make-test-python.nix {

  # Either the configuration of a single machine:
  machine =
    { config, pkgs, ... }:
    { configuration…

  # Or a set of machines:
  nodes =
    { machine1 =
        { config, pkgs, ... }: {  };
      machine2 =
        { config, pkgs, ... }: {  };

  testScript =
      Python code…

The attribute testScript is a bit of Python code that executes the test (described below). During the test, it will start one or more virtual machines, the configuration of which is described by the attribute machine (if you need only one machine in your test) or by the attribute nodes (if you need multiple machines). For instance, login.nix only needs a single machine to test whether users can log in on the virtual console, whether device ownership is correctly maintained when switching between consoles, and so on. On the other hand, nfs.nix, which tests NFS client and server functionality in the Linux kernel (including whether locks are maintained across server crashes), requires three machines: a server and two clients.

There are a few special NixOS configuration options for test VMs:


The memory of the VM in megabytes.


The virtual networks to which the VM is connected. See nat.nix for an example.


By default, the Nix store in the VM is not writable. If you enable this option, a writable union file system is mounted on top of the Nix store to make it appear writable. This is necessary for tests that run Nix operations that modify the store.

For more options, see the module qemu-vm.nix.

The test script is a sequence of Python statements that perform various actions, such as starting VMs, executing commands in the VMs, and so on. Each virtual machine is represented as an object stored in the variable name if this is also the identifier of the machine in the declarative config. If you didn't specify multiple machines using the nodes attribute, it is just machine. The following example starts the machine, waits until it has finished booting, then executes a command and checks that the output is more-or-less correct:

if not "Linux" in machine.succeed("uname"):
  raise Exception("Wrong OS")

The first line is actually unnecessary; machines are implicitly started when you first execute an action on them (such as wait_for_unit or succeed). If you have multiple machines, you can speed up the test by starting them in parallel:


The following methods are available on machine objects:


Start the virtual machine. This method is asynchronous — it does not wait for the machine to finish booting.


Shut down the machine, waiting for the VM to exit.


Simulate a sudden power failure, by telling the VM to exit immediately.


Simulate unplugging the Ethernet cable that connects the machine to the other machines.


Undo the effect of block.


Take a picture of the display of the virtual machine, in PNG format. The screenshot is linked from the HTML log.


Return a textual representation of what is currently visible on the machine's screen using optical character recognition.

Note: This requires passing enableOCR to the test attribute set.

Send a command to the QEMU monitor. This is rarely used, but allows doing stuff such as attaching virtual USB disks to a running machine.


Simulate pressing keys on the virtual keyboard, e.g., send_keys("ctrl-alt-delete").


Simulate typing a sequence of characters on the virtual keyboard, e.g., send_keys("foobar\n") will type the string foobar followed by the Enter key.


Execute a shell command, returning a list (status, stdout).


Execute a shell command, raising an exception if the exit status is not zero, otherwise returning the standard output.


Like succeed, but raising an exception if the command returns a zero status.


Repeat a shell command with 1-second intervals until it succeeds.


Repeat a shell command with 1-second intervals until it fails.


Wait until the specified systemd unit has reached the “active” state.


Wait until the specified file exists.


Wait until a process is listening on the given TCP port (on localhost, at least).


Wait until nobody is listening on the given TCP port.


Wait until the X11 server is accepting connections.


Wait until the supplied regular expressions matches the textual contents of the screen by using optical character recognition (see get_screen_text).

Note: This requires passing enableOCR to the test attribute set.

Wait until an X11 window has appeared whose name matches the given regular expression, e.g., wait_for_window("Terminal").


Copies a file from host to machine, e.g., copy_file_from_host("myfile", "/etc/my/important/file").

The first argument is the file on the host. The file needs to be accessible while building the nix derivation. The second argument is the location of the file on the machine.


Runs systemctl commands with optional support for systemctl --user

machine.systemctl("list-jobs --no-pager") # runs `systemctl list-jobs --no-pager`
machine.systemctl("list-jobs --no-pager", "any-user") # spawns a shell for `any-user` and runs `systemctl --user list-jobs --no-pager`

To test user units declared by the optional user argument can be used:

machine.wait_for_unit("xautolock.service", "x-session-user")

This applies to systemctl, get_unit_info, wait_for_unit, start_job and stop_job.

For faster dev cycles it's also possible to disable the code-linters (this shouldn't be commited though):

import ./make-test-python.nix {
  skipLint = true;
  machine =
    { config, pkgs, ... }:
    { configuration…

  testScript =
      Python code…

48.2. Running Tests

You can run tests using nix-build. For example, to run the test login.nix, you just do:

$ nix-build '<nixpkgs/nixos/tests/login.nix>'

or, if you don’t want to rely on NIX_PATH:

$ cd /my/nixpkgs/nixos/tests
$ nix-build login.nix
running the VM test script
machine: QEMU running (pid 8841)
6 out of 6 tests succeeded

After building/downloading all required dependencies, this will perform a build that starts a QEMU/KVM virtual machine containing a NixOS system. The virtual machine mounts the Nix store of the host; this makes VM creation very fast, as no disk image needs to be created. Afterwards, you can view a pretty-printed log of the test:

$ firefox result/log.html

48.3. Running Tests interactively

The test itself can be run interactively. This is particularly useful when developing or debugging a test:

$ nix-build nixos/tests/login.nix -A driver
$ ./result/bin/nixos-test-driver
starting VDE switch for network 1

You can then take any Python statement, e.g.

> start_all()
> test_script()
> machine.succeed("touch /tmp/foo")
> print(machine.succeed("pwd")) # Show stdout of command

The function test_script executes the entire test script and drops you back into the test driver command line upon its completion. This allows you to inspect the state of the VMs after the test (e.g. to debug the test script).

To just start and experiment with the VMs, run:

$ nix-build nixos/tests/login.nix -A driver
$ ./result/bin/nixos-run-vms

The script nixos-run-vms starts the virtual machines defined by test.

The machine state is kept across VM restarts in /tmp/vm-state-machinename.

Chapter 49. Testing the Installer

Building, burning, and booting from an installation CD is rather tedious, so here is a quick way to see if the installer works properly:

# mount -t tmpfs none /mnt
# nixos-generate-config --root /mnt
$ nix-build '<nixpkgs/nixos>' -A
# ./result/bin/nixos-install

To start a login shell in the new NixOS installation in /mnt:

$ nix-build '<nixpkgs/nixos>' -A
# ./result/bin/nixos-enter

Chapter 50. Releases

50.1. Release process

Going through an example of releasing NixOS 17.09:

50.1.1. One month before the beta

  • Send an email to the nix-devel mailinglist as a warning about upcoming beta "feature freeze" in a month.

  • Discuss with Eelco Dolstra and the community (via IRC, ML) about what will reach the deadline. Any issue or Pull Request targeting the release should be included in the release milestone.

50.1.2. At beta release time

50.1.3. During Beta

  • Monitor the master branch for bugfixes and minor updates and cherry-pick them to the release branch.

50.1.4. Before the final release

50.1.5. At final release time

  • git tag -s -a -m "Release 15.09" 15.09

  • Update "Chapter 4. Upgrading NixOS" section of the manual to match new stable release version.

  • Update the NIXOS_SERIES in the nixos-homepage repository.

  • Get number of commits for the release: git log release-14.04..release-14.12 --format=%an|wc -l

  • Commits by contributor: git log release-14.04..release-14.12 --format=%an|sort|uniq -c|sort -rn

  • Create a new topic on the Discourse instance to announce the release with the above information. Best to check how previous email was formulated to see what needs to be included.

50.2. Release Management Team

For each release there are two release managers. After each release the release manager having managed two releases steps down and the release management team of the last release appoints a new release manager.

This makes sure a release management team always consists of one release manager who already has managed one release and one release manager being introduced to their role, making it easier to pass on knowledge and experience.

Release managers for the current NixOS release are tracked by GitHub team @NixOS/nixos-release-managers.

A release manager's role and responsibilities are:

  • manage the release process

  • start discussions about features and changes for a given release

  • create a roadmap

  • release in cooperation with Eelco Dolstra

  • decide which bug fixes, features, etc... get backported after a release

50.3. Release schedule

Date Event
2016-07-25 Send email to nix-dev about upcoming branch-off
2016-09-01 release-16.09 branch and corresponding jobsets are created, change freeze
2016-09-30 NixOS 16.09 released