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https://github.com/SebastianWendel/nixpkgs.git
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95 lines
3.1 KiB
XML
95 lines
3.1 KiB
XML
<section xmlns="http://docbook.org/ns/docbook" xmlns:xlink="http://www.w3.org/1999/xlink" xml:id="sec-booting-via-kexec">
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<title><quote>Booting</quote> into NixOS via kexec</title>
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<para>
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In some cases, your system might already be booted into/preinstalled
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with another Linux distribution, and booting NixOS by attaching an
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installation image is quite a manual process.
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</para>
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<para>
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This is particularly useful for (cloud) providers where you can’t
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boot a custom image, but get some Debian or Ubuntu installation.
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</para>
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<para>
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In these cases, it might be easier to use <literal>kexec</literal>
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to <quote>jump into NixOS</quote> from the running system, which
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only assumes <literal>bash</literal> and <literal>kexec</literal> to
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be installed on the machine.
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</para>
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<para>
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Note that kexec may not work correctly on some hardware, as devices
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are not fully re-initialized in the process. In practice, this
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however is rarely the case.
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</para>
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<para>
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To build the necessary files from your current version of nixpkgs,
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you can run:
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</para>
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<programlisting>
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nix-build -A kexec.x86_64-linux '<nixpkgs/nixos/release.nix>'
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</programlisting>
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<para>
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This will create a <literal>result</literal> directory containing
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the following:
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</para>
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<itemizedlist spacing="compact">
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<listitem>
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<para>
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<literal>bzImage</literal> (the Linux kernel)
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</para>
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</listitem>
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<listitem>
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<para>
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<literal>initrd</literal> (the initrd file)
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</para>
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</listitem>
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<listitem>
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<para>
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<literal>kexec-boot</literal> (a shellscript invoking
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<literal>kexec</literal>)
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</para>
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</listitem>
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</itemizedlist>
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<para>
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These three files are meant to be copied over to the other already
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running Linux Distribution.
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</para>
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<para>
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Note it’s symlinks pointing elsewhere, so <literal>cd</literal> in,
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and use <literal>scp * root@$destination</literal> to copy it over,
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rather than rsync.
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</para>
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<para>
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Once you finished copying, execute <literal>kexec-boot</literal>
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<emphasis>on the destination</emphasis>, and after some seconds, the
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machine should be booting into an (ephemeral) NixOS installation
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medium.
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</para>
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<para>
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In case you want to describe your own system closure to kexec into,
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instead of the default installer image, you can build your own
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<literal>configuration.nix</literal>:
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</para>
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<programlisting language="bash">
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{ modulesPath, ... }: {
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imports = [
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(modulesPath + "/installer/netboot/netboot-minimal.nix")
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];
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services.openssh.enable = true;
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users.users.root.openssh.authorizedKeys.keys = [
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"my-ssh-pubkey"
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];
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}
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</programlisting>
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<programlisting>
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nix-build '<nixpkgs/nixos>' \
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--arg configuration ./configuration.nix
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--attr config.system.build.kexecTree
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</programlisting>
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<para>
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Make sure your <literal>configuration.nix</literal> does still
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import <literal>netboot-minimal.nix</literal> (or
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<literal>netboot-base.nix</literal>).
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</para>
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</section>
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