bug#64472: guix pull --roll-back breaks guix

bug#64472: guix pull --roll-back breaks guix

[Blake Shaw via Bug reports for GNU Guix]

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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

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bug#64472: guix pull --roll-back breaks guix

[Simon Tournier]

Hi,

Indeed, the issue can be annoying.

--8<---------------cut here---------------start------------->8---
$ guix gc ---delete-generations=0d

$ guix pull --roll-back
fetching path `/gnu/store/…-module-import-compiled'...
Downloading https://ci.guix.gnu.org/nar/lzip/…-module-import-compiled...
 module-import-compiled  107KiB       1.4MiB/s 00:00 ▕██████████████████▏ 100.0%
fetching path `/gnu/store/…-libffi-3.4.4'...
Downloading https://ci.guix.gnu.org/nar/lzip/…-libffi-3.4.4...
 libffi-3.4.4  56KiB                  6.3MiB/s 00:00 ▕██████████████████▏ 100.0%
fetching path `/gnu/store/…-libgc-8.2.2'...
Downloading https://ci.guix.gnu.org/nar/zstd/…-libgc-8.2.2...
 libgc-8.2.2  228KiB                  2.3MiB/s 00:00 ▕██████████████████▏ 100.0%
fetching path `/gnu/store/…-libunistring-1.0'...
Downloading https://ci.guix.gnu.org/nar/zstd/…-libunistring-1.0...
 libunistring-1.0  661KiB             2.7MiB/s 00:00 ▕██████████████████▏ 100.0%
fetching path `/gnu/store/…-pkg-config-0.29.2'...
Downloading https://ci.guix.gnu.org/nar/zstd/…-pkg-config-0.29.2...
 pkg-config-0.29.2  209KiB            2.3MiB/s 00:00 ▕██████████████████▏ 100.0%
fetching path `/gnu/store/…-guile-3.0.9'...
Downloading https://ci.guix.gnu.org/nar/zstd/…-guile-3.0.9...
 guile-3.0.9  8.1MiB                  1.6MiB/s 00:05 ▕██████████████████▏ 100.0%

building path(s) `/gnu/store/zm6cs3grf3l78mz1swakvfddn6k66l7m-profile'
switched from generation 29 to 0
--8<---------------cut here---------------end--------------->8---

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,

--8<---------------cut here---------------start------------->8---
$ ls -1 /var/guix/profiles/per-user/simon/ | grep current
current-guix
current-guix-0-link
current-guix-29-link
--8<---------------cut here---------------end--------------->8---

And that profile numbered 0 newly created is empty:

--8<---------------cut here---------------start------------->8---
$ tree /var/guix/profiles/per-user/simon/current-guix-0-link
/var/guix/profiles/per-user/simon/current-guix-0-link
├── etc
│   └── profile
└── manifest

2 directories, 2 files
--8<---------------cut here---------------end--------------->8---


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

> 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?

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