Comment 10 for bug 2042665

Hi,

The latter problem is unrelated to the issue at hand, as the folks at AskUbuntu have indicated it is an issue with grub-customizer, which incidentally hasn't been part of Ubuntu since *before* Jammy. Since your system used to be a Jammy one, which logically means you installed it from a third-party, e.g. a PPA. Please get in touch with whoever supplied it so that they can help you with this.

Now, that said, I can at least advise you to immediately back up your personal data before doing anything else, including attempting a reboot of the machine, since you're having issues with the bootloader.

Regarding the initial issue, there is indeed a small issue with a file that moved between libc6 and libc-dev between Lunar and Mantic without the proper metadata having been updated. However, upgrading from one version of Ubuntu to another isn't supposed to be done via the standard updater nor a simple `apt upgrade`, but rather through dedicated upgrade tooling, e.g. https://ubuntu.com/tutorials/upgrading-ubuntu-desktop#1-before-you-start for a graphical UI, or `do-release-upgrade` in a terminal.

To quickly unstuck you on the libc6/libc-dev issue, something along the lines of `sudo apt -o Dpkg::Options::="--force-overwrite" full-upgrade` should force through that part of the upgrade. However, that's a band-aid, but even assuming you manage to sort out your grub-customizer issues, you're likely to face further issues, since it appears you've tried to force the upgrade once the first problem was encountered, making it pretty hard to recover. My advice is to either restore from an earlier backup, or even simply reinstall.