For some unknown reason my NixOS update on my laptop last night failed to
properly install GRUB (even though I claim that GRUB completed
sucessfully). When I rebooted I was met with a simple grub prompt
grub>
and no boot menu.
Here is what I did to recover.
(1) I booted from a NixOS install media and logged in as root.
(2) I mounted my hard disk at /mnt:
mount /dev/sda /mnt
(3) I browsed the system profiles to select the one I wanted to reactive:
ls -l /mnt/nix/var/nix/profiles/system*
My lastest generation is system-27-link. For safety I decided I
wanted to active system-26-link.
(4) Bind dev and friends: Loosely following the nixos-install script, I
ran the following commands:
mount --rbind /dev /mnt/dev
mount --rbind /proc /mnt/proc
mount --rbind /sys /mnt/sys
(5) I reactivated the system-26-link generation
NIXOS_INSTALL_GRUB=1 chroot /mnt
/nix/var/nix/profiles/system-26-link/bin/switch-to-configuration boot
After that I rebooted, and I was fine.
This is all written from memory, so there may be errors.
Also, I didn't actually run the command in step (5). I actually ran
chroot /mnt /bin/sh
and from the shell I ran the switch-to-configuration command.
Currently, I'm too scared to try to reproduce the GRUB install failure.
--
Russell O'Connor <http://r6.ca/>
``All talk about `theft,''' the general counsel of the American Graphophone
Company wrote, ``is the merest claptrap, for there exists no property in
ideas musical, literary or artistic, except as defined by statute.''
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