Rodrigo Arias Mallo dd6d8c9735 Add documentation section about GRUB chain loading

Reviewed-by: Aleix Boné <abonerib@bsc.es>

2024-09-12 08:36:47 +02:00

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Installing NixOS in a new node

This article shows the steps to install NixOS in a node following the configuration of the repo.

Enable the serial console

By default, the nodes have the serial console disabled in the GRUB and also boot without the serial enabled.

To enable the serial console in the GRUB, set in /etc/default/grub the following lines:

GRUB_TERMINAL="console serial"
GRUB_SERIAL_COMMAND="serial --speed=115200 --unit=0 --word=8 --parity=no --stop=1"

To boot Linux with the serial enabled, so you can see the boot log and login via serial set:

GRUB_CMDLINE_LINUX="console=ttyS0,115200n8 console=tty0"

Then update the grub config:

# grub2-mkconfig -o /boot/grub2/grub.cfg

And reboot.

Prepare the disk

Create a main partition and label it nixos following the manual.

# disk=/dev/sdX
# parted $disk -- mklabel msdos
# parted $disk -- mkpart primary 1MB -8GB
# parted $disk -- mkpart primary linux-swap -8GB 100%
# parted $disk -- set 1 boot on

Then create an etx4 filesystem, labeled nixos where the system will be installed. Ensure that no other partition has the same label.

# mkfs.ext4 -L nixos "${disk}1"
# mkswap -L swap "${disk}2"
# mount ${disk}1 /mnt
# lsblk -f $disk
NAME   FSTYPE LABEL UUID                                 MOUNTPOINT
sdX
`-sdX1 ext4   nixos 10d73b75-809c-4fa3-b99d-4fab2f0d0d8e /mnt

Prepare nix and nixos-install

Mount the nix store from the hut node in read-only /nix.

# mkdir /nix
# mount -o ro hut:/nix /nix

Get the nix binary and nixos-install tool from hut:

# ssh hut 'readlink -f $(which nix)'
/nix/store/0sxbaj71c4c4n43qhdxm31f56gjalksw-nix-2.13.3/bin/nix
# ssh hut 'readlink -f $(which nixos-install)'
/nix/store/9yq8ps06ysr2pfiwiij39ny56yk3pdcs-nixos-install/bin/nixos-install

And add them to the PATH:

# export PATH=$PATH:/nix/store/0sxbaj71c4c4n43qhdxm31f56gjalksw-nix-2.13.3/bin
# export PATH=$PATH:/nix/store/9yq8ps06ysr2pfiwiij39ny56yk3pdcs-nixos-install/bin/
# nix --version
nix (Nix) 2.13.3

Adapt owl configuration

Clone owl repo:

$ git clone git@bscpm03.bsc.es:rarias/owl.git
$ cd owl

Edit the configuration to your needs.

Install from another Linux OS

Install nixOS into the storage drive.

# nixos-install --flake --root /mnt .#xeon0X

At this point, the nixOS grub has been installed into the nixos device, which is not the default boot device. To keep both the old Linux and NixOS grubs, add an entry into the old Linux grub to jump into the new grub.

# echo "

menuentry 'NixOS' {
    insmod chain
    search --no-floppy --label nixos --set root
    configfile /boot/grub/grub.cfg
} " >> /etc/grub.d/40_custom

Rebuild grub config.

# grub2-mkconfig -o /boot/grub/grub.cfg

To boot into NixOS manually, reboot and select NixOS in the grub menu to boot into NixOS.

To temporarily boot into NixOS only on the next reboot run:

# grub2-reboot 'NixOS'

To permanently boot into NixOS as the default boot OS, edit /etc/default/grub/:

GRUB_DEFAULT='NixOS'

And update grub.

# grub2-mkconfig -o /boot/grub/grub.cfg

Build the nixos kexec image

# nix build .#nixosConfigurations.xeon02.config.system.build.kexecTree -v

Chain NixOS in same disk with other systems

To install NixOS on a partition along another system which controls the GRUB, first disable the grub device, so the GRUB is not installed in the disk by NixOS (only the /boot files will be generated):

boot.loader.grub.device = "nodev";

Then add the following entry to the old GRUB configuration:

menuentry 'NixOS' {
        insmod chain
        search --no-floppy --label nixos --set root
        configfile /boot/grub/grub.cfg
}

The partition with NixOS must have the label "nixos" for it to be found. New system configuration entries will be stored in the GRUB configuration managed by NixOS, so there is no need to change the old GRUB settings.

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