guix pull --roll-back breaks guix

Hiya Guix,

I just encountered a surprising bug.

I've been trying to get the [redacted] proprietary GPU drivers to work on my system (but this isnt particular to the issue at hand), and I "guix installed" the [redacted-module] package in my .guix-profile, to see if that would help me with the failed

$ modprobe [redacted]

that I was experiencing.

It didn't, so I decided to do what we do best: roll-back. But I accidentally ran

$ guix pull --roll-back

instead of

$ guix package --roll-back

This mistake should be trivial, fixable by running

$ guix pull --switch-generation=N

Where N is the "FROM" field of the roll-back message that guix displays following a successfull roll back.

But to my surprise an anomaly appeared in the "TO" field of the roll-back message:

$ guix pull --roll-back

building path(s) `/gnu/store/2s7a7h...gj23-profile`

switched from generation 86 to 0

Huh? Zero? It should have switched to 85. Weird, but np, let's just direct it to 85.

$ guix pull --switch-generation=85

-bash: /home/my-profile/.config/guix/current/bin/guix

So now it can't find guix. Visiting .config/guix/current/ it is empty except an etc dir and a manifest. so I use guix from the run directory to get back on track:

$ exec /run/current-system/profile/bin/guix --switch-generation=85

guix pull error: cannot switch to generation '85'

$ exec /run/current-system/profile/bin/guix --switch-generation=86

switched from generation 0 to 86

And then $HOME/.config/guix/current is back to normal and everything works fine. So I assume this was due to yesterday's guix gc --delete-generations=1d

But like, should this happen? Should we ever be rolling back to an empty "0" generation that doesn't even contain guix, and thus creates a pickle for those who don't have prior knowledge of how to get out of it? Should we limit gc --delete-generations to always keep a previous generation at hand, perhaps unless forced by some other flag, so that [in particular, new] users don't break their systems in the middle of the day and then have something to solve that encumbers their plans & work?

Happy hacking!

Blake

Hi,

Indeed, the issue can be annoying.

Aside the unexpected downloads, now Guix have disappeared…

$ hash guix

$ type -P guix

/home/simon/.config/guix/profiles/emacs/emacs/bin/guix

At best it finds nothing. Or worse, it could find an unexpected one

installed in one of my profiles – here from the package ’guix’. And it

hides the error “No such file or directory”; for instance, it outputs:

$ guix describe

Generation 8 Oct 25 2023 14:23:41 (current)

guix 4dfdd82

repository URL: https://git.savannah.gnu.org/git/guix.git

branch: master

commit: 4dfdd822102690b5687acf28365ab707b68d9476

And I do not know where that comes from. Another story.

Well, the current profiles reads,

And that profile numbered 0 newly created is empty:

On Wed, 05 Jul 2023 at 17:21, Blake Shaw <blake@reproduciblemedia.com> wrote:

IMHO, it is an bug with “guix pull --roll-back”. When the current

generation is the older one, then it should not be possible to

roll-back; or roll-back should do nothing in this corner case.

It should not be possible to create an empty profile numbered 0.

Cheers,

simon