Installing NixOSObtaining NixOSNixOS ISO images can be downloaded from the NixOS
homepage. These can be burned onto a CD. It is also possible
to copy them onto a USB stick and install NixOS from there. For
details, see 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
homepage.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.InstallationBoot from the CD.The CD contains a basic NixOS installation. (It
also contains Memtest86+, useful if you want to test new hardware.)
When it’s finished booting, it should have detected most of your
hardware and brought up networking (check
ifconfig). 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.The NixOS manual is available on virtual console 8
(press Alt+F8 to access).Login as root and the empty
password.If you downloaded the graphical ISO image, you can
run start display-manager to start KDE.The NixOS installer doesn’t do any partitioning or
formatting yet, so you need to that yourself. Use the following
commands:
For partitioning:
fdisk.For initialising Ext4 partitions:
mkfs.ext4. It is recommended that you assign a
unique symbolic label to the file system using the option
, since this
makes the file system configuration independent from device
changes. For example:
$ mkfs.ext4 -L nixos /dev/sda1For creating swap partitions:
mkswap. Again it’s recommended to assign a
label to the swap partition: .For creating LVM volumes, the LVM commands, e.g.,
$ pvcreate /dev/sda1 /dev/sdb1
$ vgcreate MyVolGroup /dev/sda1 /dev/sdb1
$ lvcreate --size 2G --name bigdisk MyVolGroup
$ lvcreate --size 1G --name smalldisk MyVolGroupFor creating software RAID devices, use
mdadm.Mount the target file system on which NixOS should
be installed on /mnt, e.g.
$ mount /dev/disk/by-label/nixos /mnt
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.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 , while a
list of available configuration options appears in . A minimal example is shown in .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
The vim text editor is also available.You must set the option
to specify on which disk
the GRUB boot loader is to be installed. Without it, NixOS cannot
boot.Another critical option is ,
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.)Depending on your hardware configuration or type of
file system, you may need to set the option
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 CD 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.Examples of real-world NixOS configuration files can be
found at .Do the installation:
$ nixos-install
Cross fingers. If this fails due to a temporary problem (such as
a network issue while downloading binaries from the NixOS binary
cache), you can just re-run nixos-install.
Otherwise, fix your configuration.nix and
then re-run nixos-install.If everything went well:
$ rebootYou 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 ), a new item appears in the menu.
This allows you to easily roll back to another 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 eelcoYou may also want to install some software. For instance,
$ nix-env -qa \*
shows what packages are available, and
$ nix-env -i w3m
install the w3m browser.To summarise, shows a
typical sequence of commands for installing NixOS on an empty hard
drive (here /dev/sda). shows a corresponding configuration Nix expression.Commands for installing NixOS on <filename>/dev/sda</filename>
$ fdisk /dev/sda # (or whatever device you want to install on)
$ mkfs.ext4 -L nixos /dev/sda1
$ mkswap -L swap /dev/sda2
$ swapon /dev/sda2
$ mount /dev/disk/by-label/nixos /mnt
$ nixos-generate-config --root /mnt
$ nano /mnt/etc/nixos/configuration.nix
$ nixos-install
$ rebootNixOS configuration
{ config, pkgs, ... }:
{
imports =
[ # Include the results of the hardware scan.
./hardware-configuration.nix
];
boot.loader.grub.device = "/dev/sda";
# 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;
}UEFI InstallationNixOS can also be installed on UEFI systems. The procedure
is by and large the same as a BIOS installation, with the following
changes:
You should boot the live CD in UEFI mode (consult your
specific hardware's documentation for instructions).Instead of fdisk, you should use
gdisk to partition your disks. You will need to
have a separate partition for /boot with
partition code EF00, and it should be formatted as a
vfat filesystem.You must set to
true, and
to false. 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
and
as well.To see console messages during early boot, add "fbcon"
to your .Booting from a USB stickFor systems withoua CD drive, the NixOS livecd can be booted from
a usb stick. For non-UEFI installations,
unetbootin
will work. For UEFI installations, you should mount the ISO, copy its contents
verbatim to your drive, then either:
Change the label of the disk partition to the label of the ISO
(visible with the blkid command), orEdit loader/entries/nixos-livecd.conf on the drive
and change the root= field in the options
line to point to your drive (see the documentation on root=
in
the kernel documentation for more details).Changing the configurationThe file /etc/nixos/configuration.nix
contains the current configuration of your machine. Whenever you’ve
changed something to 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).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. 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
Upgrading NixOSThe 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-13.10.
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 3.4.66 to 3.4.67 (a minor bug fix), but
not from 3.4.x to
3.11.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.
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.)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 13.10 ISO, you will be subscribed to
the nixos-13.10 channel. To see which NixOS
channel you’re subscribed to, run the following as root:
$ nix-channel --list | grep nixos
nixos https://nixos.org/channels/nixos-unstable
To switch to a different NixOS channel, do
$ nix-channel --add http://nixos.org/channels/channel-name nixos
(Be sure to include the nixos parameter at the
end.) For instance, to use the NixOS 13.10 stable channel:
$ nix-channel --add http://nixos.org/channels/nixos-13.10 nixos
But it you want to live on the bleeding edge:
$ nix-channel --add http://nixos.org/channels/nixos-unstable 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.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.