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<section
xmlns="http://docbook.org/ns/docbook"
xmlns:xlink="http://www.w3.org/1999/xlink"
xmlns:xi="http://www.w3.org/2001/XInclude"
version="5.0"
xml:id="sec-installing-from-other-distro">
<title>Installing from another Linux distribution</title>
<para>
Because Nix (the package manager) &amp; 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:
</para>
<orderedlist>
<listitem>
<para>
Install NixOS on another partition, from your existing Linux distribution
(without the use of a USB or optical device!)
</para>
</listitem>
<listitem>
<para>
Install NixOS on the same partition (in place!), from your existing
non-NixOS Linux distribution using <literal>NIXOS_LUSTRATE</literal>.
</para>
</listitem>
<listitem>
<para>
Install NixOS on your hard drive from the Live CD of any Linux
distribution.
</para>
</listitem>
</orderedlist>
<para>
The first steps to all these are the same:
</para>
<orderedlist>
<listitem>
<para>
Install the Nix package manager:
</para>
<para>
Short version:
</para>
<screen>
<prompt>$ </prompt>curl -L https://nixos.org/nix/install | sh
<prompt>$ </prompt>. $HOME/.nix-profile/etc/profile.d/nix.sh # …or open a fresh shell</screen>
<para>
More details in the
<link
xlink:href="https://nixos.org/nix/manual/#chap-quick-start">
Nix manual</link>
</para>
</listitem>
<listitem>
<para>
Switch to the NixOS channel:
</para>
<para>
If you've just installed Nix on a non-NixOS distribution, you will be on
the <literal>nixpkgs</literal> channel by default.
</para>
<screen>
<prompt>$ </prompt>nix-channel --list
nixpkgs https://nixos.org/channels/nixpkgs-unstable</screen>
<para>
As that channel gets released without running the NixOS tests, it will be
safer to use the <literal>nixos-*</literal> channels instead:
</para>
<screen>
<prompt>$ </prompt>nix-channel --add https://nixos.org/channels/nixos-<replaceable>version</replaceable> nixpkgs</screen>
<para>
You may want to throw in a <literal>nix-channel --update</literal> for good
measure.
</para>
</listitem>
<listitem>
<para>
Install the NixOS installation tools:
</para>
<para>
You'll need <literal>nixos-generate-config</literal> and
<literal>nixos-install</literal> and we'll throw in some man pages and
<literal>nixos-enter</literal> 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..
</para>
<screen><prompt>$ </prompt>nix-env -f '&lt;nixpkgs/nixos&gt;' --arg configuration {} -iA config.system.build.{nixos-generate-config,nixos-install,nixos-enter,manual.manpages}</screen>
</listitem>
<listitem>
<note>
<para>
The following 5 steps are only for installing NixOS to another partition.
For installing NixOS in place using <literal>NIXOS_LUSTRATE</literal>,
skip ahead.
</para>
</note>
<para>
Prepare your target partition:
</para>
<para>
At this point it is time to prepare your target partition. Please refer to
the partitioning, file-system creation, and mounting steps of
<xref linkend="sec-installation" />
</para>
<para>
If you're about to install NixOS in place using
<literal>NIXOS_LUSTRATE</literal> there is nothing to do for this step.
</para>
</listitem>
<listitem>
<para>
Generate your NixOS configuration:
</para>
<screen><prompt>$ </prompt>sudo `which nixos-generate-config` --root /mnt</screen>
<para>
You'll probably want to edit the configuration files. Refer to the
<literal>nixos-generate-config</literal> step in
<xref
linkend="sec-installation" /> for more
information.
</para>
<para>
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 <literal>configuration.nix</literal>:
</para>
<programlisting>
<xref linkend="opt-boot.loader.grub.extraEntries"/> = ''
menuentry "Ubuntu" {
search --set=ubuntu --fs-uuid 3cc3e652-0c1f-4800-8451-033754f68e6e
configfile "($ubuntu)/boot/grub/grub.cfg"
}
'';</programlisting>
<para>
(You can find the appropriate UUID for your partition in
<literal>/dev/disk/by-uuid</literal>)
</para>
</listitem>
<listitem>
<para>
Create the <literal>nixbld</literal> group and user on your original
distribution:
</para>
<screen>
<prompt>$ </prompt>sudo groupadd -g 30000 nixbld
<prompt>$ </prompt>sudo useradd -u 30000 -g nixbld -G nixbld nixbld</screen>
</listitem>
<listitem>
<para>
Download/build/install NixOS:
</para>
<warning>
<para>
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.
</para>
</warning>
<screen><prompt>$ </prompt>sudo PATH="$PATH" NIX_PATH="$NIX_PATH" `which nixos-install` --root /mnt</screen>
<para>
Again, please refer to the <literal>nixos-install</literal> step in
<xref linkend="sec-installation" /> for more information.
</para>
<para>
That should be it for installation to another partition!
</para>
</listitem>
<listitem>
<para>
Optionally, you may want to clean up your non-NixOS distribution:
</para>
<screen>
<prompt>$ </prompt>sudo userdel nixbld
<prompt>$ </prompt>sudo groupdel nixbld</screen>
<para>
If you do not wish to keep the Nix package manager installed either, run
something like <literal>sudo rm -rv ~/.nix-* /nix</literal> and remove the
line that the Nix installer added to your <literal>~/.profile</literal>.
</para>
</listitem>
<listitem>
<note>
<para>
The following steps are only for installing NixOS in place using
<literal>NIXOS_LUSTRATE</literal>:
</para>
</note>
<para>
Generate your NixOS configuration:
</para>
<screen><prompt>$ </prompt>sudo `which nixos-generate-config` --root /</screen>
<para>
Note that this will place the generated configuration files in
<literal>/etc/nixos</literal>. You'll probably want to edit the
configuration files. Refer to the <literal>nixos-generate-config</literal>
step in <xref
linkend="sec-installation" /> for more
information.
</para>
<para>
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 <literal>sudo passwd -l root</literal> if you
use <literal>sudo</literal>)
</para>
<programlisting>
<link linkend="opt-users.users._name_.initialHashedPassword">users.users.root.initialHashedPassword</link> = "";
</programlisting>
</listitem>
<listitem>
<para>
Build the NixOS closure and install it in the <literal>system</literal>
profile:
</para>
<screen><prompt>$ </prompt>nix-env -p /nix/var/nix/profiles/system -f '&lt;nixpkgs/nixos&gt;' -I nixos-config=/etc/nixos/configuration.nix -iA system</screen>
</listitem>
<listitem>
<para>
Change ownership of the <literal>/nix</literal> tree to root (since your
Nix install was probably single user):
</para>
<screen><prompt>$ </prompt>sudo chown -R 0.0 /nix</screen>
</listitem>
<listitem>
<para>
Set up the <literal>/etc/NIXOS</literal> and
<literal>/etc/NIXOS_LUSTRATE</literal> files:
</para>
<para>
<literal>/etc/NIXOS</literal> officializes that this is now a NixOS
partition (the bootup scripts require its presence).
</para>
<para>
<literal>/etc/NIXOS_LUSTRATE</literal> tells the NixOS bootup scripts to
move <emphasis>everything</emphasis> that's in the root partition to
<literal>/old-root</literal>. 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:
</para>
<itemizedlist>
<listitem>
<para>
The <literal>/nix</literal> directory
</para>
</listitem>
<listitem>
<para>
The <literal>/boot</literal> directory
</para>
</listitem>
<listitem>
<para>
Any file or directory listed in <literal>/etc/NIXOS_LUSTRATE</literal>
(one per line)
</para>
</listitem>
</itemizedlist>
<note>
<para>
Support for <literal>NIXOS_LUSTRATE</literal> was added in NixOS 16.09.
The act of "lustrating" refers to the wiping of the existing distribution.
Creating <literal>/etc/NIXOS_LUSTRATE</literal> can also be used on NixOS
to remove all mutable files from your root partition (anything that's not
in <literal>/nix</literal> or <literal>/boot</literal> gets "lustrated" on
the next boot.
</para>
<para>
lustrate /ˈlʌstreɪt/ verb.
</para>
<para>
purify by expiatory sacrifice, ceremonial washing, or some other ritual
action.
</para>
</note>
<para>
Let's create the files:
</para>
<screen>
<prompt>$ </prompt>sudo touch /etc/NIXOS
<prompt>$ </prompt>sudo touch /etc/NIXOS_LUSTRATE
</screen>
<para>
Let's also make sure the NixOS configuration files are kept once we reboot
on NixOS:
</para>
<screen>
<prompt>$ </prompt>echo etc/nixos | sudo tee -a /etc/NIXOS_LUSTRATE
</screen>
</listitem>
<listitem>
<para>
Finally, move the <literal>/boot</literal> 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:
</para>
<warning>
<para>
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.
</para>
</warning>
<screen>
<prompt>$ </prompt>sudo mv -v /boot /boot.bak &amp;&amp;
sudo /nix/var/nix/profiles/system/bin/switch-to-configuration boot
</screen>
<para>
Cross your fingers, reboot, hopefully you should get a NixOS prompt!
</para>
</listitem>
<listitem>
<para>
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:
</para>
<screen>
# 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</screen>
<para>
This may work as is or you might also need to reinstall the boot loader
</para>
<para>
And of course, if you're happy with NixOS and no longer need the old
distribution:
</para>
<screen>sudo rm -rf /old-root</screen>
</listitem>
<listitem>
<para>
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,
<link
xlink:href="https://github.com/elitak/nixos-infect">nixos-infect</link>
uses the lustrate process to convert Digital Ocean droplets to NixOS from
other distributions automatically.
</para>
</listitem>
</orderedlist>
</section>