Forcing pacman to perform post-upgrade tasks if it's failed part way through
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You know it's not a great start to your week when, after a long weekend, you set your work laptop running through updates and it crashes part-way through the install process. After a reboot, it ends up not even detecting Arch's install, and only allows you to reboot into the BIOS 😅
So I started frantically searching around "how to recover a failed pacman install" (and other words to that effect) while getting my installation medium booted as a recovery disk, at which point I found "Fixing an unbootable system caused by an interrupted upgrade" on the Arch Wiki, as well as some Arch Linux forum posts to the same effect.
Unfortunately these didn't seem to work, and I couldn't see a full list of the packages that pacman had upgraded as part of this morning's view - at least in a super straightforward means - but clicked through to the "talk" page which noted github.com/edu4rdshl/archlinux-pkgrecover.
Fortunately, this is what I was able to use to resolve my local 👏🏼
To do this, I needed to:
Look for the "last known good" upgrade in /var/log/pacman.log, before today's date:
...
[2024-09-03T11:16:49+0100] [PACMAN] Running 'pacman -D -q --asexplicit --config /etc/pacman.conf -- xdo'
[2024-09-09T08:03:23+0100] [PACMAN] Running 'pacman -S -y --config /etc/pacman.conf --'
...
In this case, we can see that 2024-09-03 was the last upgrade.
Then, I ran archlinux-pkgrecover like so:
bash ./pkgrecover.sh --pacman-db 2024-09-03 ../pacman.log-fail-boot --dry-run
This ended up doing what I needed (despite the --dry-run flag) and re-installed every package that had been updated since 2024-09-03, and then ran through the post-upgrade hooks.
Once done, I was able to successfully reboot into my install.
Note that you should make sure you have at a minimum your / and /boot (or EFI) partitions mounted, depending on how your system is set up.
(Aside: Arch Linux is continually incredibly stable for me and it's largely this specific device which has known issues...)
