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xmlns="http://docbook.org/ns/docbook"
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xmlns:xlink="http://www.w3.org/1999/xlink"
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xmlns:xi="http://www.w3.org/2001/XInclude"
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xml:id="sec-installing-from-other-distro">
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<title>Installing from another Linux distribution</title>
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Because Nix (the package manager) & Nixpkgs (the Nix packages
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collection) can both be installed on any (most?) Linux distributions,
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they can be used to install NixOS in various creative ways. You can,
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<listitem><para>Install NixOS on another partition, from your existing
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Linux distribution (without the use of a USB or optical
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device!)</para></listitem>
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<listitem><para>Install NixOS on the same partition (in place!), from
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your existing non-NixOS Linux distribution using
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<literal>NIXOS_LUSTRATE</literal>.</para></listitem>
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<listitem><para>Install NixOS on your hard drive from the Live CD of
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any Linux distribution.</para></listitem>
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<para>The first steps to all these are the same:</para>
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<para>Install the Nix package manager:</para>
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<para>Short version:</para>
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$ bash <(curl https://nixos.org/nix/install)
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$ . $HOME/.nix-profile/etc/profile.d/nix.sh # …or open a fresh shell</screen>
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<para>More details in the <link
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xlink:href="https://nixos.org/nix/manual/#chap-quick-start">
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Nix manual</link></para>
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<para>Switch to the NixOS channel:</para>
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<para>If you've just installed Nix on a non-NixOS distribution, you
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will be on the <literal>nixpkgs</literal> channel by
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$ nix-channel --list
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nixpkgs https://nixos.org/channels/nixpkgs-unstable</screen>
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<para>As that channel gets released without running the NixOS
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tests, it will be safer to use the <literal>nixos-*</literal>
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channels instead:</para>
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$ nix-channel --add https://nixos.org/channels/nixos-<replaceable>version</replaceable> nixpkgs</screen>
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<para>You may want to throw in a <literal>nix-channel
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--update</literal> for good measure.</para>
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<para>Install the NixOS installation tools:</para>
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<para>You'll need <literal>nixos-generate-config</literal> and
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<literal>nixos-install</literal> and we'll throw in some man
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pages and <literal>nixos-enter</literal> just in case you want
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to chroot into your NixOS partition. They are installed by
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default on NixOS, but you don't have NixOS yet..</para>
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<screen>$ nix-env -iE "_: with import <nixpkgs/nixos> { configuration = {}; }; with config.system.build; [ nixos-generate-config nixos-install nixos-enter manual.manpages ]"</screen>
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<note><para>The following 5 steps are only for installing NixOS to
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another partition. For installing NixOS in place using
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<literal>NIXOS_LUSTRATE</literal>, skip ahead.</para></note>
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<para>Prepare your target partition:</para>
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<para>At this point it is time to prepare your target partition.
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Please refer to the partitioning, file-system creation, and
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mounting steps of <xref linkend="sec-installation" /></para>
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<para>If you're about to install NixOS in place using
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<literal>NIXOS_LUSTRATE</literal> there is nothing to do for
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<para>Generate your NixOS configuration:</para>
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<screen>$ sudo `which nixos-generate-config` --root /mnt</screen>
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<para>You'll probably want to edit the configuration files. Refer
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to the <literal>nixos-generate-config</literal> step in <xref
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linkend="sec-installation" /> for more information.</para>
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<para>Consider setting up the NixOS bootloader to give you the
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ability to boot on your existing Linux partition. For instance,
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if you're using GRUB and your existing distribution is running
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Ubuntu, you may want to add something like this to your
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<literal>configuration.nix</literal>:</para>
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boot.loader.grub.extraEntries = ''
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menuentry "Ubuntu" {
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search --set=ubuntu --fs-uuid 3cc3e652-0c1f-4800-8451-033754f68e6e
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configfile "($ubuntu)/boot/grub/grub.cfg"
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'';</programlisting>
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<para>(You can find the appropriate UUID for your partition in
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<literal>/dev/disk/by-uuid</literal>)</para>
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<para>Create the <literal>nixbld</literal> group and user on your
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original distribution:</para>
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$ sudo groupadd -g 30000 nixbld
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$ sudo useradd -u 30000 -g nixbld -G nixbld nixbld</screen>
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<para>Download/build/install NixOS:</para>
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<warning><para>Once you complete this step, you might no longer be
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able to boot on existing systems without the help of a
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rescue USB drive or similar.</para></warning>
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<screen>$ sudo PATH="$PATH" NIX_PATH="$NIX_PATH" `which nixos-install` --root /mnt</screen>
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<para>Again, please refer to the <literal>nixos-install</literal>
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step in <xref linkend="sec-installation" /> for more
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information.</para>
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<para>That should be it for installation to another partition!</para>
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<para>Optionally, you may want to clean up your non-NixOS distribution:</para>
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$ sudo userdel nixbld
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$ sudo groupdel nixbld</screen>
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<para>If you do not wish to keep the Nix package mananager
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installed either, run something like <literal>sudo rm -rv
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~/.nix-* /nix</literal> and remove the line that the Nix
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installer added to your <literal>~/.profile</literal>.</para>
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<note><para>The following steps are only for installing NixOS in
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<literal>NIXOS_LUSTRATE</literal>:</para></note>
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<para>Generate your NixOS configuration:</para>
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<screen>$ sudo `which nixos-generate-config` --root /</screen>
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<para>Note that this will place the generated configuration files
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in <literal>/etc/nixos</literal>. You'll probably want to edit
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the configuration files. Refer to the
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<literal>nixos-generate-config</literal> step in <xref
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linkend="sec-installation" /> for more information.</para>
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<para>You'll likely want to set a root password for your first boot
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using the configuration files because you won't have a chance
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to enter a password until after you reboot. You can initalize
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the root password to an empty one with this line: (and of course
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don't forget to set one once you've rebooted or to lock the
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account with <literal>sudo passwd -l root</literal> if you use
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<literal>sudo</literal>)</para>
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<programlisting>users.extraUsers.root.initialHashedPassword = "";</programlisting>
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<para>Build the NixOS closure and install it in the
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<literal>system</literal> profile:</para>
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<screen>$ nix-env -p /nix/var/nix/profiles/system -f '<nixpkgs/nixos>' -I nixos-config=/etc/nixos/configuration.nix -iA system</screen>
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<para>Change ownership of the <literal>/nix</literal> tree to root
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(since your Nix install was probably single user):</para>
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<screen>$ sudo chown -R 0.0 /nix</screen>
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<para>Set up the <literal>/etc/NIXOS</literal> and
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<literal>/etc/NIXOS_LUSTRATE</literal> files:</para>
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<para><literal>/etc/NIXOS</literal> officializes that this is now a
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NixOS partition (the bootup scripts require its presence).</para>
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<para><literal>/etc/NIXOS_LUSTRATE</literal> tells the NixOS bootup
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scripts to move <emphasis>everything</emphasis> that's in the
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root partition to <literal>/old-root</literal>. This will move
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your existing distribution out of the way in the very early
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stages of the NixOS bootup. There are exceptions (we do need to
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keep NixOS there after all), so the NixOS lustrate process will
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<listitem><para>The <literal>/nix</literal>
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directory</para></listitem>
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<listitem><para>The <literal>/boot</literal>
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directory</para></listitem>
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<listitem><para>Any file or directory listed in
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<literal>/etc/NIXOS_LUSTRATE</literal> (one per
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line)</para></listitem>
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<para>Let's create the files:</para>
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$ sudo touch /etc/NIXOS
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$ sudo touch /etc/NIXOS_LUSTRATE</screen>
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<para>Let's also make sure the NixOS configuration files are kept
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once we reboot on NixOS:</para>
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$ echo etc/nixos | sudo tee -a /etc/NIXOS_LUSTRATE</screen>
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<para>Finally, move the <literal>/boot</literal> directory of your
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current distribution out of the way (the lustrate process will
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take care of the rest once you reboot, but this one must be
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moved out now because NixOS needs to install its own boot
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<warning><para>Once you complete this step, your current
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distribution will no longer be bootable! If you didn't get
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all the NixOS configuration right, especially those
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settings pertaining to boot loading and root partition,
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NixOS may not be bootable either. Have a USB rescue device
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ready in case this happens. </para></warning>
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$ sudo mv -v /boot /boot.bak &&
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sudo /nix/var/nix/profiles/system/bin/switch-to-configuration boot</screen>
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<para>Cross your fingers, reboot, hopefully you should get a NixOS
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<para>If for some reason you want to revert to the old
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distribution, you'll need to boot on a USB rescue disk and do
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something along these lines:</para>
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# mount /dev/sdaX root
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# mkdir root/nixos-root
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# mv -v root/* root/nixos-root/
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# mv -v root/nixos-root/old-root/* root/
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# mv -v root/boot.bak root/boot # We had renamed this by hand earlier
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<para>This may work as is or you might also need to reinstall the
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<para>And of course, if you're happy with NixOS and no longer need
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the old distribution:</para>
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<screen>sudo rm -rf /old-root</screen>
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<para>It's also worth noting that this whole process can be
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automated. This is especially useful for Cloud VMs, where
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provider do not provide NixOS. For instance, <link
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xlink:href="https://github.com/elitak/nixos-infect">nixos-infect</link>
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uses the lustrate process to convert Digital Ocean droplets to
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NixOS from other distributions automatically.</para>
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