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65 lines
2.0 KiB
Markdown
65 lines
2.0 KiB
Markdown
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# "Booting" into NixOS via kexec {#sec-booting-via-kexec}
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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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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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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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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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To build the necessary files from your current version of nixpkgs,
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you can run:
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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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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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These three files are meant to be copied over to the other already running
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Linux Distribution.
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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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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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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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```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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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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```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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Make sure your `configuration.nix` does still import `netboot-minimal.nix` (or
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`netboot-base.nix`).
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