When installing NixOS in the target filesystem /mnt, paths relative to
configuration.nix in `initrd.secrets` are turned by Nix into absolute
paths that reference /mnt. While building the system derivation works,
installing the bootloader fails because the latter process takes place
inside the chroot environment where /mnt does not exist.
Ideally, we would also build the system within chroot, but this greatly
complicates the matter as it requires manually copying over Nix, its
runtime dependencies and all channels. Possibly, this would also break
several assumptions users have about how nixos-install works.
A simpler and safer (but less neat) solution is to temporarily bind
mount all mount points in /mnt under /mnt/mnt to keep the paths
functional while the bootloader is being installed.
This is essentially the workaround described in issue #73404.
The build of initrd-secrets can routinely fail for old boot entries
if the secrets have been removed or renamed in a later generation.
This always happens for generation 1, because it's built from the
NixOS installer and the paths differs by the mount point (i.e. /mnt).
The error is very confusing because it fails to mention it's about
an older generation and that it's somewhat harmless.
This commit turns the error into a warning for all generations but the
current, adds the name of the failed entry to the message and a note
explaining why it can happen.
This commit fixes a papercut in nixos-rebuild where people wanting to
switch to a specialisation (or test one) were forced to manually figure
out the specialisation's path and run its activation script - since now,
there's a dedicated option to do just that.
This is a backwards-compatible change which doesn't affect the existing
behavior, which - to be fair - might still be considered sus by some
people, the painful scenario here being:
- you boot into specialisation `foo`,
- you run `nixos-rebuild switch`,
- whoops, you're no longer at specialisation `foo`, but you're rather
brought back to the base system.
(it's especially painful for cases where specialisation is used to load
extra drivers, e.g. Nvidia, since then launching `nixos-rebuild switch`,
while forgetting that you're inside a specialisation, can cause some
parts of your system to get accidentally unloaded.)
I've tried to mitigate that by improving specialisations so that they
create a dedicated file somewhere in `/run/current-system` containing
the specialisation's name (which `nixos-rebuild` could then use as the
default value for `--specialisation`), but I haven't been able to come
up with anything working (plus it would be a breaking change then).
Closes https://github.com/NixOS/nixpkgs/issues/174065
