Florian Klink
2 years ago
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cdaaf95e20
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<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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|
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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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@ -0,0 +1,64 @@ |
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# "Booting" into NixOS via kexec {#sec-booting-via-kexec} |
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|
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In some cases, your system might already be booted into/preinstalled with |
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another Linux distribution, and booting NixOS by attaching an installation |
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image is quite a manual process. |
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|
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This is particularly useful for (cloud) providers where you can't boot a custom |
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image, but get some Debian or Ubuntu installation. |
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|
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In these cases, it might be easier to use `kexec` to "jump into NixOS" from the |
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running system, which only assumes `bash` and `kexec` to be installed on the |
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machine. |
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|
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Note that kexec may not work correctly on some hardware, as devices are not |
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fully re-initialized in the process. In practice, this however is rarely the |
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case. |
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|
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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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|
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```ShellSession |
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nix-build -A kexec.x86_64-linux '<nixpkgs/nixos/release.nix>' |
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``` |
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|
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This will create a `result` directory containing the following: |
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- `bzImage` (the Linux kernel) |
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- `initrd` (the initrd file) |
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- `kexec-boot` (a shellscript invoking `kexec`) |
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|
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These three files are meant to be copied over to the other already running |
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Linux Distribution. |
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|
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Note it's symlinks pointing elsewhere, so `cd` in, and use |
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`scp * root@$destination` to copy it over, rather than rsync. |
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|
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Once you finished copying, execute `kexec-boot` *on the destination*, and after |
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some seconds, the machine should be booting into an (ephemeral) NixOS |
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installation medium. |
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|
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In case you want to describe your own system closure to kexec into, instead of |
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the default installer image, you can build your own `configuration.nix`: |
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|
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```nix |
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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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|
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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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``` |
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|
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|
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```ShellSession |
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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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``` |
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|
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Make sure your `configuration.nix` does still import `netboot-minimal.nix` (or |
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`netboot-base.nix`). |
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