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nike

Installing nixos with justdoit. @cleverca22 came up with all of this, wrote the justdoit.nix file, and showed me how to use it. This repo is just a condensed version with some documentation showing others how to use it. Users of this should know that it is extremely unsafe and it is possible to brick the target system.

The Goal

  • Install NixOS with justdoit, a convenience script that takes care of a lot of nitty-gritty system setup for you, especially if you are using zfs.

The steps, at a high level

  • Define a NixOS configuration that can be built into a bootable NixOS ramdisk for any server with a linux kernel that has kexec enabled
  • Define a NixOS configuration that gets placed onto the target host, which gets used by nixos-install (invoked by justdoit)
  • Deploy the NixOS ramdisk to the server
  • Boot from that ramdisk
  • Run justdoit
  • Profit

What you will need

  • A source machine running Linux/MacOS with Nix installed. You will need to enable flakes and nix-command.
  • A target machine running the Linux kernel with kexec enabled.

Configure the NixOS ramdisk

Edit configuration.nix to your liking. Necessary things:

  1. Imports (netboot-minimal.nix, kexec.nix, justdoit.nix)
  2. Networking. You can use wpa\_supplicant or network manager.
  3. authorized ssh keys for the root user. This is so you can ssh to the machine after booting the NixOS ramdisk.
  4. Configure kexec.justdoit. See justdoit.nix for available options. This will require knowing things about the target system, most of which you can find out via fdisk -l.
  5. importing autoreboot.nix is not necessary, HOWEVER, it is a useful safety net. If the network isn't working on kexec, it will be impossible to recover the machine. Autoreboot will reboot automatically at the end of each hour. It needs to be stopped immediately before executing justdoit. See the example provided configuration.nix for reference.

Configure the target config

Edit target-config.nix to your liking. This will be the resulting configuration on the new system after justdoit has finished and NixOS has been forcibly installed on the target. You will probably want networking and ssh keys on this, but it's not necessary unless you don't have physical access to the machine. You can use an existing NixOS configuration for this (e.g. your NixOS config). Know that it should import ./hardware-configuration.nix and ./generated.nix, but these are files that are generated by justdoit, and not things you should provide. See the example provided target-config.nix for reference.

Build the kexec tarball

$ nix build '.#nixosConfigurations.nike.config.system.build.kexec_tarball' -j4

Deploy the tarball to the target machine and install NixOS

[chessai@source-nixos:~/nike]$ nix build '.#nixosConfigurations.nike.config.system.build.kexec_tarball' -j4
[chessai@source-nixos:~/nike]$ export TARGET_IP=<some_ip>
[chessai@source-nixos:~/nike]$ scp result/tarball/nixos-system-x86_64-linux.tar.xz $TARGET_IP:.
[chessai@source-nixos:~/nike]$ ssh $TARGET_IP

[chessai@target-ubuntu:~]$ sudo -i
[sudo] password for chessai:
[root@target-ubuntu:~]# cd /
[root@target-ubuntu:/]# tar -xf /home/chessai/nixos-system-x86_64-linux.tar.xz
[root@target-ubuntu:/]# ./kexec_nixos
executing kernel, filesystems will be improperly unmounted
Connection to $TARGET_IP closed.

[chessai@source-nixos:~/nike]$ ping $TARGET_IP
PING $TARGET_IP ($TARGET_IP) 56(84) bytes of data.
64 bytes from $TARGET_IP: icmp_seq=1 ttl=64 time=0.197 ms
64 bytes from $TARGET_IP: icmp_seq=2 ttl=64 time=0.121 ms
64 bytes from $TARGET_IP: icmp_seq=3 ttl=64 time=0.181 ms
^C
[chessai@source-nixos:~/nike]$ ssh root@$TARGET_IP
The authenticity of host '$TARGET_IP ($TARGET_IP)' can't be established.
ED25519 key fingerprint is SHA256:o1Tl49CuK6Ipd5gT6GaNfotsgVMJcdxr2FZbGrmhqmE.
Are you sure you want to continue connecting (yes/no)? yes
Warning: Permanently added '$TARGET_IP' (ED25519) to the list of known hosts.
Last login: Fri Dec  9 05:47:11 2016

[root@kexec:~]# wpa_passphrase $SSID $PASSWORD >> /etc/wpa_supplicant.conf
[root@kexec:~]# systemctl restart wpa_supplicant.service
[root@kexec:~]# systemctl stop autoreboot.timer
[root@kexec:~]# justdoit
[root@kexec:~]# shutdown -r now