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# Building Images with `nixos-rebuild build-image` {#sec-image-nixos-rebuild-build-image}
Nixpkgs contains a variety of modules to build custom images for different virtualization platforms and cloud providers, such as e.g. `amazon-image.nix` and `proxmox-lxc.nix`.
While those can be imported directly, `system.build.images` provides an attribute set mapping variant names to image derivations. Available variants are defined - end extendable - in `image.modules`, an attribute set mapping variant names to NixOS modules.
All of those images can be built via both, their `system.build.image` attribute and the `nixos-rebuild build-image` command.
For example, to build an Amazon image from your existing NixOS configuration, run:
```ShellSession
$ nixos-rebuild build-image --image-variant amazon
[...]
Done. The disk image can be found in /nix/store/[hash]-nixos-image-amazon-25.05pre-git-x86_64-linux/nixos-image-amazon-25.05pre-git-x86_64-linux.vpc
```
To get a list of all variants available, run `nixos-rebuild build-image` without arguments.
::: {.example #ex-nixos-rebuild-build-image-customize}
## Customize specific image variants {#sec-image-nixos-rebuild-build-image-customize}
The `image.modules` option can be used to set specific options per image variant, in a similar fashion as [specialisations](options.html#opt-specialisation) for generic NixOS configurations.
E.g. images for the cloud provider Linode use `grub2` as a bootloader by default. If you are using `systemd-boot` on other platforms and want to disable it for Linode only, you could use the following options:
``` nix
{
image.modules.linode = {
boot.loader.systemd-boot.enable = lib.mkForce false;
};
}
```

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# Building Images via `systemd-repart` {#sec-image-repart}
You can build disk images in NixOS with the `image.repart` option provided by
the module [image/repart.nix][]. This module uses `systemd-repart` to build the
images and exposes it's entire interface via the `repartConfig` option.
[image/repart.nix]: https://github.com/NixOS/nixpkgs/blob/master/nixos/modules/image/repart.nix
An example of how to build an image:
```nix
{ config, modulesPath, ... }:
{
imports = [ "${modulesPath}/image/repart.nix" ];
image.repart = {
name = "image";
partitions = {
"esp" = {
contents = {
# ...
};
repartConfig = {
Type = "esp";
# ...
};
};
"root" = {
storePaths = [ config.system.build.toplevel ];
repartConfig = {
Type = "root";
Label = "nixos";
# ...
};
};
};
};
}
```
## Nix Store Paths {#sec-image-repart-store-paths}
If you want to rewrite Nix store paths, e.g., to remove the `/nix/store` prefix
or to nest it below a parent path, you can do that through the
`nixStorePrefix` option.
### Nix Store Partition {#sec-image-repart-store-partition}
You can define a partition that only contains the Nix store and then mount it
under `/nix/store`. Because the `/nix/store` part of the paths is already
determined by the mount point, you have to set `nixStorePrefix = "/"` so
that `/nix/store` is stripped from the paths before copying them into the image.
```nix
{
fileSystems."/nix/store".device = "/dev/disk/by-partlabel/nix-store";
image.repart.partitions = {
"store" = {
storePaths = [ config.system.build.toplevel ];
nixStorePrefix = "/";
repartConfig = {
Type = "linux-generic";
Label = "nix-store";
# ...
};
};
};
}
```
### Nix Store Subvolume {#sec-image-repart-store-subvolume}
Alternatively, you can create a Btrfs subvolume `/@nix-store` containing the
Nix store and mount it on `/nix/store`:
```nix
{
fileSystems."/" = {
device = "/dev/disk/by-partlabel/root";
fsType = "btrfs";
options = [ "subvol=/@" ];
};
fileSystems."/nix/store" = {
device = "/dev/disk/by-partlabel/root";
fsType = "btrfs";
options = [ "subvol=/@nix-store" ];
};
image.repart.partitions = {
"root" = {
storePaths = [ config.system.build.toplevel ];
nixStorePrefix = "/@nix-store";
repartConfig = {
Type = "root";
Label = "root";
Format = "btrfs";
Subvolumes = "/@ /@nix-store";
MakeDirectories = "/@ /@nix-store";
# ...
};
};
};
}
```
## Appliance Image {#sec-image-repart-appliance}
The `image/repart.nix` module can also be used to build self-contained [software
appliances][].
[software appliances]: https://en.wikipedia.org/wiki/Software_appliance
The generation based update mechanism of NixOS is not suited for appliances.
Updates of appliances are usually either performed by replacing the entire
image with a new one or by updating partitions via an A/B scheme. See the
[Chrome OS update process][chrome-os-update] for an example of how to achieve
this. The appliance image built in the following example does not contain a
`configuration.nix` and thus you will not be able to call `nixos-rebuild` from
this system. Furthermore, it uses a [Unified Kernel Image][unified-kernel-image].
[chrome-os-update]: https://chromium.googlesource.com/aosp/platform/system/update_engine/+/HEAD/README.md
[unified-kernel-image]: https://uapi-group.org/specifications/specs/unified_kernel_image/
```nix
let
pkgs = import <nixpkgs> { };
efiArch = pkgs.stdenv.hostPlatform.efiArch;
in
(pkgs.nixos [
(
{
config,
lib,
pkgs,
modulesPath,
...
}:
{
imports = [ "${modulesPath}/image/repart.nix" ];
boot.loader.grub.enable = false;
fileSystems."/".device = "/dev/disk/by-label/nixos";
image.repart = {
name = "image";
partitions = {
"esp" = {
contents = {
"/EFI/BOOT/BOOT${lib.toUpper efiArch}.EFI".source =
"${pkgs.systemd}/lib/systemd/boot/efi/systemd-boot${efiArch}.efi";
"/EFI/Linux/${config.system.boot.loader.ukiFile}".source =
"${config.system.build.uki}/${config.system.boot.loader.ukiFile}";
};
repartConfig = {
Type = "esp";
Format = "vfat";
SizeMinBytes = "96M";
};
};
"root" = {
storePaths = [ config.system.build.toplevel ];
repartConfig = {
Type = "root";
Format = "ext4";
Label = "nixos";
Minimize = "guess";
};
};
};
};
}
)
]).image
```

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# Building a NixOS (Live) ISO {#sec-building-image}
Default live installer configurations are available inside `nixos/modules/installer/cd-dvd`.
For building other system images, see [Building Images with `nixos-rebuild build-image`](#sec-image-nixos-rebuild-build-image).
You have two options:
- Use any of those default configurations as is
- Combine them with (any of) your host config(s)
System images, such as the live installer ones, know how to enforce configuration settings
on which they immediately depend in order to work correctly.
However, if you are confident, you can opt to override those
enforced values with `mkForce`.
## Practical Instructions {#sec-building-image-instructions}
To build an ISO image for the channel `nixos-unstable`:
```ShellSession
$ git clone https://github.com/NixOS/nixpkgs.git
$ cd nixpkgs/nixos
$ git switch nixos-unstable
$ nix-build -A config.system.build.isoImage -I nixos-config=modules/installer/cd-dvd/installation-cd-minimal.nix default.nix
```
To check the content of an ISO image, mount it like so:
```ShellSession
# mount -o loop -t iso9660 ./result/iso/nixos-image-25.05pre-git-x86_64-linux.iso /mnt/iso
```
## Additional drivers or firmware {#sec-building-image-drivers}
If you need additional (non-distributable) drivers or firmware in the
installer, you might want to extend these configurations.
For example, to build the GNOME graphical installer ISO, but with support for
certain WiFi adapters present in some MacBooks, you can create the following
file at `modules/installer/cd-dvd/installation-cd-graphical-gnome-macbook.nix`:
```nix
{ config, ... }:
{
imports = [ ./installation-cd-graphical-gnome.nix ];
boot.initrd.kernelModules = [ "wl" ];
boot.kernelModules = [
"kvm-intel"
"wl"
];
boot.extraModulePackages = [ config.boot.kernelPackages.broadcom_sta ];
}
```
Then build it like in the example above:
```ShellSession
$ git clone https://github.com/NixOS/nixpkgs.git
$ cd nixpkgs/nixos
$ export NIXPKGS_ALLOW_UNFREE=1
$ nix-build -A config.system.build.isoImage -I nixos-config=modules/installer/cd-dvd/installation-cd-graphical-gnome-macbook.nix default.nix
```
## Technical Notes {#sec-building-image-tech-notes}
The config value enforcement is implemented via `mkImageMediaOverride = mkOverride 60;`
and therefore primes over simple value assignments, but also yields to `mkForce`.
This property allows image designers to implement in semantically correct ways those
configuration values upon which the correct functioning of the image depends.
For example, the iso base image overrides those file systems which it needs at a minimum
for correct functioning, while the installer base image overrides the entire file system
layout because there can't be any other guarantees on a live medium than those given
by the live medium itself. The latter is especially true before formatting the target
block device(s). On the other hand, the netboot iso only overrides its minimum dependencies
since netboot images are always made-to-target.

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# Changing the Configuration {#sec-changing-config}
The file `/etc/nixos/configuration.nix` contains the current
configuration of your machine. Whenever you've [changed
something](#ch-configuration) in that file, you should do
```ShellSession
# 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](#opt-systemd.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
```ShellSession
# 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
```ShellSession
# 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.
```ShellSession
# 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.
A repl, or read-eval-print loop, is also available. You can inspect your configuration and use the Nix language with
```ShellSession
# nixos-rebuild repl
```
Your configuration is loaded into the `config` variable. Use tab for autocompletion, use the `:r` command to reload the configuration files. See `:?` or [`nix repl` in the Nix manual](https://nixos.org/manual/nix/stable/command-ref/new-cli/nix3-repl.html) to learn more.
Finally, you can do
```ShellSession
$ 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
```ShellSession
$ 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:
```nix
{ 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):
```ShellSession
$ QEMU_NET_OPTS="hostfwd=tcp:127.0.0.1:2222-:22" ./result/bin/run-*-vm
```
allowing you to log in via SSH (assuming you have set the appropriate
passwords or SSH authorized keys):
```ShellSession
$ ssh -p 2222 localhost
```
Such port forwardings connect via the VM's virtual network interface.
Thus they cannot connect to ports that are only bound to the VM's
loopback interface (`127.0.0.1`), and the VM's NixOS firewall
must be configured to allow these connections.

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# Installation {#ch-installation}
This section describes how to obtain, install, and configure NixOS for first-time use.
```{=include=} chapters
obtaining.chapter.md
installing.chapter.md
changing-config.chapter.md
upgrading.chapter.md
building-nixos.chapter.md
building-images-via-nixos-rebuild-build-image.chapter.md
building-images-via-systemd-repart.chapter.md
```

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# Installing behind a proxy {#sec-installing-behind-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.
```nix
{
networking.proxy.default = "http://user:password@proxy:port/";
networking.proxy.noProxy = "127.0.0.1,localhost,internal.domain";
}
```
1. Setup the proxy environment variables in the shell where you are
running `nixos-install`.
```ShellSession
# 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 `specialisation` option in `configuration.nix` to switch proxies at
runtime. Refer to [](#ch-options) for more information.
:::

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# Installing from another Linux distribution {#sec-installing-from-other-distro}
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!)
1. Install NixOS on the same partition (in place!), from your existing
non-NixOS Linux distribution using `NIXOS_LUSTRATE`.
1. 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:
```ShellSession
$ curl -L https://nixos.org/nix/install | sh
$ . $HOME/.nix-profile/etc/profile.d/nix.sh # …or open a fresh shell
```
More details in the [ Nix
manual](https://nixos.org/nix/manual/#chap-quick-start)
1. 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.
```ShellSession
$ nix-channel --list
nixpkgs https://channels.nixos.org/nixpkgs-unstable
```
As that channel gets released without running the NixOS tests, it
will be safer to use the `nixos-*` channels instead:
```ShellSession
$ nix-channel --add https://channels.nixos.org/nixos-<version> nixpkgs
```
Where `<version>` corresponds to the latest version available on [channels.nixos.org](https://channels.nixos.org/).
You may want to throw in a `nix-channel --update` for good measure.
1. Install the NixOS installation tools:
You'll need `nixos-generate-config` and `nixos-install`, but this
also makes some man pages and `nixos-enter` available, just in case
you want to chroot into your NixOS partition. NixOS installs these
by default, but you don't have NixOS yet..
```ShellSession
$ nix-env -f '<nixpkgs>' -iA nixos-install-tools
```
1. ::: {.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 [](#sec-installation)
If you're about to install NixOS in place using `NIXOS_LUSTRATE`
there is nothing to do for this step.
1. Generate your NixOS configuration:
```ShellSession
$ sudo `which nixos-generate-config` --root /mnt
```
You'll probably want to edit the configuration files. Refer to the
`nixos-generate-config` step in [](#sec-installation) 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`:
```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`)
1. Create the `nixbld` group and user on your original distribution:
```ShellSession
$ sudo groupadd -g 30000 nixbld
$ sudo useradd -u 30000 -g nixbld -G nixbld nixbld
```
1. 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.
:::
::: {.note}
On some distributions there are separate PATHS for programs intended
only for root. In order for the installation to succeed, you might
have to use `PATH="$PATH:/usr/sbin:/sbin"` in the following command.
:::
```ShellSession
$ sudo PATH="$PATH" `which nixos-install` --root /mnt
```
Again, please refer to the `nixos-install` step in
[](#sec-installation) for more information.
That should be it for installation to another partition!
1. Optionally, you may want to clean up your non-NixOS distribution:
```ShellSession
$ 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`.
1. ::: {.note}
The following steps are only for installing NixOS in place using
`NIXOS_LUSTRATE`:
:::
Generate your NixOS configuration:
```ShellSession
$ sudo `which nixos-generate-config`
```
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
[](#sec-installation) for more information.
::: {.note}
On [UEFI](https://en.wikipedia.org/wiki/UEFI) systems, check that your `/etc/nixos/hardware-configuration.nix` did the right thing with the [EFI System Partition](https://en.wikipedia.org/wiki/EFI_system_partition).
In NixOS, by default, both [systemd-boot](https://systemd.io/BOOT/) and [grub](https://www.gnu.org/software/grub/index.html) expect it to be mounted on `/boot`.
However, the configuration generator bases its [](#opt-fileSystems) configuration on the current mount points at the time it is run.
If the current system and NixOS's bootloader configuration don't agree on where the [EFI System Partition](https://en.wikipedia.org/wiki/EFI_system_partition) is to be mounted, you'll need to manually alter the mount point in `hardware-configuration.nix` before building the system closure.
:::
::: {.note}
The lustrate process will not work if the [](#opt-boot.initrd.systemd.enable) option is set to `true`.
If you want to use this option, wait until after the first boot into the NixOS system to enable it and rebuild.
:::
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 initialize 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`)
```nix
{ users.users.root.initialHashedPassword = ""; }
```
1. Build the NixOS closure and install it in the `system` profile:
```ShellSession
$ nix-env -p /nix/var/nix/profiles/system -f '<nixpkgs/nixos>' -I nixos-config=/etc/nixos/configuration.nix -iA system
```
1. Change ownership of the `/nix` tree to root (since your Nix install
was probably single user):
```ShellSession
$ sudo chown -R 0:0 /nix
```
1. 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)
::: {.note}
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:
```ShellSession
$ 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:
```ShellSession
$ echo etc/nixos | sudo tee -a /etc/NIXOS_LUSTRATE
```
1. Finally, install NixOS's boot system, backing up the current boot system's files in the process.
The details of this step can vary depending on the bootloader configuration in NixOS and the bootloader in use by the current system.
The commands below should work for:
- [BIOS](https://en.wikipedia.org/wiki/BIOS) systems.
- [UEFI](https://en.wikipedia.org/wiki/UEFI) systems where both the current system and NixOS mount the [EFI System Partition](https://en.wikipedia.org/wiki/EFI_system_partition) on `/boot`.
Both [systemd-boot](https://systemd.io/BOOT/) and [grub](https://www.gnu.org/software/grub/index.html) expect this by default in NixOS, but other distributions vary.
::: {.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.
:::
::: {.warning}
On [UEFI](https://en.wikipedia.org/wiki/UEFI) systems, anything on the [EFI System Partition](https://en.wikipedia.org/wiki/EFI_system_partition) will be removed by these commands, such as other coexisting OS's bootloaders.
:::
```ShellSession
$ sudo mkdir /boot.bak && sudo mv /boot/* /boot.bak &&
sudo NIXOS_INSTALL_BOOTLOADER=1 /nix/var/nix/profiles/system/bin/switch-to-configuration boot
```
Cross your fingers, reboot, hopefully you should get a NixOS prompt!
In other cases, most commonly where the [EFI System Partition](https://en.wikipedia.org/wiki/EFI_system_partition) of the current system is instead mounted on `/boot/efi`, the goal is to:
- Make sure `/boot` (and the [EFI System Partition](https://en.wikipedia.org/wiki/EFI_system_partition), if mounted elsewhere) are mounted how the NixOS configuration would mount them.
- Clear them of files related to the current system, backing them up outside of `/boot`.
NixOS will move the backups into `/old-root` along with everything else when it first boots.
- Instruct the NixOS closure built earlier to install its bootloader with:
```ShellSession
sudo NIXOS_INSTALL_BOOTLOADER=1 /nix/var/nix/profiles/system/bin/switch-to-configuration boot
```
1. 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:
```ShellSession
# 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:
```ShellSession
sudo rm -rf /old-root
```
1. 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](https://github.com/elitak/nixos-infect) uses the
lustrate process to convert Digital Ocean droplets to NixOS from
other distributions automatically.

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# "Booting" into NixOS via kexec {#sec-booting-via-kexec}
In some cases, your system might already be booted into/preinstalled with
another Linux distribution, and booting NixOS by attaching an installation
image is quite a manual process.
This is particularly useful for (cloud) providers where you can't boot a custom
image, but get some Debian or Ubuntu installation.
In these cases, it might be easier to use `kexec` to "jump into NixOS" from the
running system, which only assumes `bash` and `kexec` to be installed on the
machine.
Note that kexec may not work correctly on some hardware, as devices are not
fully re-initialized in the process. In practice, this however is rarely the
case.
To build the necessary files from your current version of nixpkgs,
you can run:
```ShellSession
nix-build -A kexec.x86_64-linux '<nixpkgs/nixos/release.nix>'
```
This will create a `result` directory containing the following:
- `bzImage` (the Linux kernel)
- `initrd` (the initrd file)
- `kexec-boot` (a shellscript invoking `kexec`)
These three files are meant to be copied over to the other already running
Linux Distribution.
Note its symlinks pointing elsewhere, so `cd` in, and use
`scp * root@$destination` to copy it over, rather than rsync.
Once you finished copying, execute `kexec-boot` *on the destination*, and after
some seconds, the machine should be booting into an (ephemeral) NixOS
installation medium.
In case you want to describe your own system closure to kexec into, instead of
the default installer image, you can build your own `configuration.nix`:
```nix
{ modulesPath, ... }:
{
imports = [ (modulesPath + "/installer/netboot/netboot-minimal.nix") ];
services.openssh.enable = true;
users.users.root.openssh.authorizedKeys.keys = [ "my-ssh-pubkey" ];
}
```
```ShellSession
nix-build '<nixpkgs/nixos>' \
--arg configuration ./configuration.nix
--attr config.system.build.kexecTree
```
Make sure your `configuration.nix` does still import `netboot-minimal.nix` (or
`netboot-base.nix`).

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# Booting from the "netboot" media (PXE) {#sec-booting-from-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 want to add the NixOS installer as another
option. To build the necessary files from your current version of nixpkgs,
you can run:
```ShellSession
nix-build -A netboot.x86_64-linux '<nixpkgs/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.

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# Booting from a USB flash drive {#sec-booting-from-usb}
The image has to be written verbatim to the USB flash drive for it to be
bootable on UEFI and BIOS systems. Here are the recommended tools to do that.
## Creating bootable USB flash drive with a graphical tool {#sec-booting-from-usb-graphical}
Etcher is a popular and user-friendly tool. It works on Linux, Windows and macOS.
Download it from [balena.io](https://www.balena.io/etcher/), start the program,
select the downloaded NixOS ISO, then select the USB flash drive and flash it.
::: {.warning}
Etcher reports errors and usage statistics by default, which can be disabled in
the settings.
:::
An alternative is [USBImager](https://bztsrc.gitlab.io/usbimager),
which is very simple and does not connect to the internet. Download the version
with write-only (wo) interface for your system. Start the program,
select the image, select the USB flash drive and click "Write".
## Creating bootable USB flash drive from a Terminal on Linux {#sec-booting-from-usb-linux}
1. Plug in the USB flash drive.
2. Find the corresponding device with `lsblk`. You can distinguish them by
their size.
3. Make sure all partitions on the device are properly unmounted. Replace `sdX`
with your device (e.g. `sdb`).
```ShellSession
sudo umount /dev/sdX*
```
4. Then use the `dd` utility to write the image to the USB flash drive.
```ShellSession
sudo dd bs=4M conv=fsync oflag=direct status=progress if=<path-to-image> of=/dev/sdX
```
## Creating bootable USB flash drive from a Terminal on macOS {#sec-booting-from-usb-macos}
1. Plug in the USB flash drive.
2. Find the corresponding device with `diskutil list`. You can distinguish them
by their size.
3. Make sure all partitions on the device are properly unmounted. Replace `diskX`
with your device (e.g. `disk1`).
```ShellSession
diskutil unmountDisk diskX
```
4. Then use the `dd` utility to write the image to the USB flash drive.
```ShellSession
sudo dd if=<path-to-image> of=/dev/rdiskX bs=4m
```
After `dd` completes, a GUI dialog "The disk
you inserted was not readable by this computer" will pop up, which can
be ignored.
::: {.note}
Using the 'raw' `rdiskX` device instead of `diskX` with dd completes in
minutes instead of hours.
:::
5. Eject the disk when it is finished.
```ShellSession
diskutil eject /dev/diskX
```

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# Installing in a VirtualBox guest {#sec-installing-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 set
up a VirtualBox guest, follow these instructions:
1. Add a New Machine in VirtualBox with OS Type "Linux / Other Linux"
1. Base Memory Size: 768 MB or higher.
1. New Hard Disk of 10 GB or higher.
1. Mount the CD-ROM with the NixOS ISO (by clicking on CD/DVD-ROM)
1. Click on Settings / System / Processor and enable PAE/NX
1. Click on Settings / System / Acceleration and enable "VT-x/AMD-V"
acceleration
1. Click on Settings / Display / Screen and select VMSVGA as Graphics
Controller
1. 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:
```nix
{ 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 `*`.
```nix
{ 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 not boot properly.
```nix
{ config, pkgs, ... }:
{
fileSystems."/virtualboxshare" = {
fsType = "vboxsf";
device = "nameofthesharedfolder";
options = [
"rw"
"nofail"
];
};
}
```
The folder will be available directly under the root directory.

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# Installing NixOS {#sec-installation}
## Booting from the install medium {#sec-installation-booting}
To begin the installation, you have to boot your computer from the install drive.
1. Plug in the install drive. Then turn on or restart your computer.
2. Open the boot menu by pressing the appropriate key, which is usually shown
on the display on early boot.
Select the USB flash drive (the option usually contains the word "USB").
If you choose the incorrect drive, your computer will likely continue to
boot as normal. In that case restart your computer and pick a
different drive.
::: {.note}
The key to open the boot menu is different across computer brands and even
models. It can be [F12]{.keycap}, but also [F1]{.keycap},
[F9]{.keycap}, [F10]{.keycap}, [Enter]{.keycap}, [Del]{.keycap},
[Esc]{.keycap} or another function key. If you are unsure and don't see
it on the early boot screen, you can search online for your computers
brand, model followed by "boot from usb".
The computer might not even have that feature, so you have to go into the
BIOS/UEFI settings to change the boot order. Again, search online for
details about your specific computer model.
For Apple computers with Intel processors press and hold the [⌥]{.keycap}
(Option or Alt) key until you see the boot menu. On Apple silicon press
and hold the power button.
:::
::: {.note}
If your computer supports both BIOS and UEFI boot, choose the UEFI option.
You will likely need to disable "Secure Boot" to use the UEFI option. The exact steps vary by device manufacturer but generally "Secure Boot" will be listed under "Boot", "Security" or "Advanced" in the BIOS/UEFI menu.
:::
::: {.note}
If you use a CD for the installation, the computer will probably boot from
it automatically. If not, choose the option containing the word "CD" from
the boot menu.
:::
3. Shortly after selecting the appropriate boot drive, you should be
presented with a menu with different installer options. Leave the default
and wait (or press [Enter]{.keycap} to speed up).
4. The graphical images will start their corresponding desktop environment
and the graphical installer, which can take some time. The minimal images
will boot to a command line. You have to follow the instructions in
[](#sec-installation-manual) there.
## Graphical Installation {#sec-installation-graphical}
The graphical installer is recommended for desktop users and will guide you
through the installation.
1. In the "Welcome" screen, you can select the language of the Installer and
the installed system.
::: {.tip}
Leaving the language as "American English" will make it easier to search for
error messages in a search engine or to report an issue.
:::
2. Next you should choose your location to have the timezone set correctly.
You can actually click on the map!
::: {.note}
The installer will use an online service to guess your location based on
your public IP address.
:::
3. Then you can select the keyboard layout. The default keyboard model should
work well with most desktop keyboards. If you have a special keyboard or
notebook, your model might be in the list. Select the language you are most
comfortable typing in.
4. On the "Users" screen, you have to type in your display name, login name
and password. You can also enable an option to automatically login to the
desktop.
5. Then you have the option to choose a desktop environment. If you want to
create a custom setup with a window manager, you can select "No desktop".
::: {.tip}
If you don't have a favorite desktop and don't know which one to choose,
you can stick to either GNOME or Plasma. They have a quite different
design, so you should choose whichever you like better.
They are both popular choices and well tested on NixOS.
:::
6. You have the option to allow unfree software in the next screen.
7. The easiest option in the "Partitioning" screen is "Erase disk", which will
delete all data from the selected disk and install the system on it.
Also select "Swap (with Hibernation)" in the dropdown below it.
You have the option to encrypt the whole disk with LUKS.
::: {.note}
At the top left you see if the Installer was booted with BIOS or UEFI. If
you know your system supports UEFI and it shows "BIOS", reboot with the
correct option.
:::
::: {.warning}
Make sure you have selected the correct disk at the top and that no
valuable data is still on the disk! It will be deleted when
formatting the disk.
:::
8. Check the choices you made in the "Summary" and click "Install".
::: {.note}
The installation takes about 15 minutes. The time varies based on the
selected desktop environment, internet connection speed and disk write speed.
:::
9. When the install is complete, remove the USB flash drive and
reboot into your new system!
## Manual Installation {#sec-installation-manual}
NixOS can be installed on BIOS or UEFI systems. The procedure for a UEFI
installation is broadly the same as for a BIOS installation. The differences
are mentioned in the following steps.
The NixOS manual is available by running `nixos-help` in the command line
or from the application menu in the desktop environment.
To have access to the command line on the graphical images, open
Terminal (GNOME) or Konsole (Plasma) from the application menu.
You are logged-in automatically as `nixos`. The `nixos` user account has
an empty password so you can use `sudo` without a password:
```ShellSession
$ sudo -i
```
You can use `loadkeys` to switch to your preferred keyboard layout.
(We even provide neo2 via `loadkeys de neo`!)
If the text is too small to be legible, try `setfont ter-v32n` to
increase the font size.
To install over a serial port connect with `115200n8` (e.g.
`picocom -b 115200 /dev/ttyUSB0`). When the bootloader lists boot
entries, select the serial console boot entry.
### Networking in the installer {#sec-installation-manual-networking}
[]{#sec-installation-booting-networking} <!-- legacy anchor -->
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 `ip`.
You can configure the network, Wi-Fi included, through NetworkManager.
Using the `nmtui` program, you can do so even in a non-graphical session.
If you prefer to configure the network manually, disable NetworkManager with
`systemctl stop NetworkManager`.
If you would like to continue the installation from a different machine
you can use activated SSH daemon. You need to copy your ssh key to
either `/home/nixos/.ssh/authorized_keys` or
`/root/.ssh/authorized_keys` (Tip: For installers with a modifiable
filesystem such as the sd-card installer image a key can be manually
placed by mounting the image on a different machine). Alternatively you
must set a password for either `root` or `nixos` with `passwd` to be
able to login.
### Partitioning and formatting {#sec-installation-manual-partitioning}
[]{#sec-installation-partitioning} <!-- legacy anchor -->
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`.
Use the command 'lsblk' to find the name of your 'disk' device.
The recommended partition scheme differs depending if the computer uses
*Legacy Boot* or *UEFI*.
#### UEFI (GPT) {#sec-installation-manual-partitioning-UEFI}
[]{#sec-installation-partitioning-UEFI} <!-- legacy anchor -->
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.
```ShellSession
# 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.
```ShellSession
# parted /dev/sda -- mkpart root ext4 512MB -8GB
```
3. Next, add a *swap* partition. The size required will vary according
to needs, here a 8GB one is created.
```ShellSession
# parted /dev/sda -- mkpart swap linux-swap -8GB 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.
```ShellSession
# parted /dev/sda -- mkpart ESP fat32 1MB 512MB
# parted /dev/sda -- set 3 esp on
```
::: {.note}
In case you decided to not create a swap partition, replace `3` by `2`. To be sure of the id number of ESP, run `parted --list`.
:::
Once complete, you can follow with
[](#sec-installation-manual-partitioning-formatting).
#### Legacy Boot (MBR) {#sec-installation-manual-partitioning-MBR}
[]{#sec-installation-partitioning-MBR} <!-- legacy anchor -->
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.
```ShellSession
# parted /dev/sda -- mklabel msdos
```
2. Add the *root* partition. This will fill the disk except for the
end part, where the swap will live.
```ShellSession
# parted /dev/sda -- mkpart primary 1MB -8GB
```
3. Set the root partition's boot flag to on. This allows the disk to be booted from.
```ShellSession
# parted /dev/sda -- set 1 boot on
```
4. Finally, add a *swap* partition. The size required will vary
according to needs, here a 8GB one is created.
```ShellSession
# parted /dev/sda -- mkpart primary linux-swap -8GB 100%
```
::: {.note}
The swap partition size rules are no different than for other Linux
distributions.
:::
Once complete, you can follow with
[](#sec-installation-manual-partitioning-formatting).
#### Formatting {#sec-installation-manual-partitioning-formatting}
[]{#sec-installation-partitioning-formatting} <!-- legacy anchor -->
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:
```ShellSession
# 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:
```ShellSession
# 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:
```ShellSession
# 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`.
### Installing {#sec-installation-manual-installing}
[]{#sec-installation-installing} <!-- legacy anchor -->
1. Mount the target file system on which NixOS should be installed on
`/mnt`, e.g.
```ShellSession
# mount /dev/disk/by-label/nixos /mnt
```
2. **UEFI systems**
Mount the boot file system on `/mnt/boot`, e.g.
```ShellSession
# mkdir -p /mnt/boot
# mount -o umask=077 /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.
```ShellSession
# 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 [](#sec-configuration-syntax),
while a list of available configuration options appears in
[](#ch-options). A minimal example is shown in
[Example: NixOS Configuration](#ex-config).
This command accepts an optional `--flake` option, to also generate a
`flake.nix` file, if you want to set up a flake-based configuration.
The command `nixos-generate-config` can generate an initial
configuration file for you:
```ShellSession
# nixos-generate-config --root /mnt
```
You should then edit `/mnt/etc/nixos/configuration.nix` to suit your
needs:
```ShellSession
# 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 [](#opt-boot.loader.grub.device) to
specify on which disk the GRUB boot loader is to be installed.
Without it, NixOS cannot boot.
If there are other operating systems running on the machine before
installing NixOS, the [](#opt-boot.loader.grub.useOSProber)
option can be set to `true` to automatically add them to the grub
menu.
UEFI systems
: You must select a boot-loader, either systemd-boot or GRUB. The recommended
option is systemd-boot: set the option [](#opt-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`](#opt-boot.loader.efi.canTouchEfiVariables) and
[`boot.loader.systemd-boot`](#opt-boot.loader.systemd-boot.enable)
as well.
If you want to use GRUB, set [](#opt-boot.loader.grub.device) to `nodev` and
[](#opt-boot.loader.grub.efiSupport) to `true`.
With systemd-boot, you should not need any special configuration to detect
other installed systems. With GRUB, set [](#opt-boot.loader.grub.useOSProber)
to `true`, but this will only detect windows partitions, not other Linux
distributions. If you dual boot another Linux distribution, use systemd-boot
instead.
If you need to configure networking for your machine the
configuration options are described in [](#sec-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](https://github.com/NixOS/nixos-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:
```ShellSession
# 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`.
If you opted for a flake-based configuration, you will need to pass the
`--flake` here as well and specify the name of the configuration as used in
the `flake.nix` file. For the default generated flake, this is `nixos`.
```ShellSession
# nixos-install --flake 'path/to/flake.nix#nixos'
```
As the last step, `nixos-install` will ask you to set the password
for the `root` user, e.g.
```plain
setting root password...
New password: ***
Retype new password: ***
```
If you have a user account declared in your `configuration.nix` and plan to log in using this user, set a password before rebooting, e.g. for the `alice` user:
```ShellSession
# nixos-enter --root /mnt -c 'passwd alice'
```
::: {.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:
```ShellSession
# 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](#sec-changing-config)), a new item is added to the
menu. This allows you to easily roll back to a previous
configuration if something goes wrong.
Use your declared user account to log in.
If you didn’t declare one, you should still be able to log in using the `root` user.
::: {.note}
Some graphical display managers such as SDDM do not allow `root` login by default, so you might need to switch to TTY.
Refer to [](#sec-user-management) for details on declaring user accounts.
:::
You may also want to install some software. This will be covered in
[](#sec-package-management).
### Installation summary {#sec-installation-manual-summary}
[]{#sec-installation-summary} <!-- legacy anchor -->
To summarise, [Example: Commands for Installing NixOS on `/dev/sda`](#ex-install-sequence)
shows a typical sequence of commands for installing NixOS on an empty hard
drive (here `/dev/sda`). [Example: NixOS Configuration](#ex-config) shows a
corresponding configuration Nix expression.
::: {#ex-partition-scheme-MBR .example}
### Example partition schemes for NixOS on `/dev/sda` (MBR)
```ShellSession
# parted /dev/sda -- mklabel msdos
# parted /dev/sda -- mkpart primary 1MB -8GB
# parted /dev/sda -- mkpart primary linux-swap -8GB 100%
```
:::
::: {#ex-partition-scheme-UEFI .example}
### Example partition schemes for NixOS on `/dev/sda` (UEFI)
```ShellSession
# parted /dev/sda -- mklabel gpt
# parted /dev/sda -- mkpart root ext4 512MB -8GB
# parted /dev/sda -- mkpart swap linux-swap -8GB 100%
# parted /dev/sda -- mkpart ESP fat32 1MB 512MB
# parted /dev/sda -- set 3 esp on
```
:::
::: {#ex-install-sequence .example}
### Commands for Installing NixOS on `/dev/sda`
With a partitioned disk.
```ShellSession
# 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 -o umask=077 /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
```
:::
::: {#ex-config .example}
### Example: NixOS Configuration
```ShellSession
{ config, pkgs, ... }: {
imports = [
# Include the results of the hardware scan.
./hardware-configuration.nix
];
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;
}
```
:::
## Additional installation notes {#sec-installation-additional-notes}
```{=include=} sections
installing-usb.section.md
installing-pxe.section.md
installing-kexec.section.md
installing-virtualbox-guest.section.md
installing-from-other-distro.section.md
installing-behind-a-proxy.section.md
```

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# Obtaining NixOS {#sec-obtaining}
NixOS ISO images can be downloaded from the [NixOS download
page](https://nixos.org/download.html#nixos-iso). Follow the instructions in
[](#sec-booting-from-usb) to create a bootable USB flash drive.
If you have a very old system that can't boot from USB, you can burn the image
to an empty CD. NixOS might not work very well on such systems.
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](https://nixos.org/download.html#nixos-virtualbox).
- Using AMIs for Amazon's EC2. To find one for your region, please refer
to the [download page](https://nixos.org/download.html#nixos-amazon).
- 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](https://nixos.org/nixops) for details.

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# Upgrading NixOS {#sec-upgrading}
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 a selection of packages has been built successfully
(see `nixos/release-combined.nix` and `nixos/release-small.nix`).
These channels are:
- *Stable channels*, such as [`nixos-25.11`](https://channels.nixos.org/nixos-25.11).
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`](https://channels.nixos.org/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-25.11-small`](https://channels.nixos.org/nixos-25.11-small)
or [`nixos-unstable-small`](https://channels.nixos.org/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 <https://channels.nixos.org>.
(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 <https://nixos.org/download/> 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 25.11 ISO, you will be subscribed to
the `nixos-25.11` channel. To see which NixOS channel you're subscribed
to, run the following as root:
```ShellSession
# nix-channel --list | grep nixos
nixos https://channels.nixos.org/nixos-unstable
```
To switch to a different NixOS channel, do
```ShellSession
# nix-channel --add https://channels.nixos.org/channel-name nixos
```
(Be sure to include the `nixos` parameter at the end.) For instance, to
use the NixOS 25.05 stable channel:
```ShellSession
# nix-channel --add https://channels.nixos.org/nixos-25.11 nixos
```
If you have a server, you may want to use the "small" channel instead:
```ShellSession
# nix-channel --add https://channels.nixos.org/nixos-25.11-small nixos
```
And if you want to live on the bleeding edge:
```ShellSession
# nix-channel --add https://channels.nixos.org/nixos-unstable nixos
```
You can then upgrade NixOS to the latest version in your chosen channel
by running
```ShellSession
# 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.
:::
## Automatic Upgrades {#sec-upgrading-automatic}
You can keep a NixOS system up-to-date automatically by adding the
following to `configuration.nix`:
```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.
```nix
{ system.autoUpgrade.channel = "https://channels.nixos.org/nixos-25.11"; }
```