Backup LVM snapshots and Grub2 problem

It looks like grub-mount is trying to edit a read only file system and has hung.

It should be safe to send a signal with kill to ask it to give up (send 15, and if needed after a few seconds 2, and if needed after a few seconds 1, if it's still running use -9 and report it to the maintainer) (if the pid number changes start with 15 again )

It's likely to exit non-zero which may effect scripts waiting on it, but the only thing you can do about that is file a bug report and ask the maintainer to have it skip read only file systems.

Note that there are some related bugs they are working on.

Just kill that leftover grub-mount process. This happened to me as well, and there was no apparent negative side-effect to the killing, because the relevant update-grub process had already abandoned it - you can easily verify that by seeing how it the leftover grub-mount process no longer has a parent.