I have a Ubuntu 24.04.2 system where /dev/shm gets remounted (I assume) every now and then (roughly each 10 seconds), but I have no idea why. There's no mention of that mounting point in /etc/fstab and even if I would add an entry in there it would still be remounted with other options than the one I expect.
Here's the output from /proc/self/mountinfo (see final column):
$ while true; do column -t -N mountID,parentID,"major:minor",rootMount,mountPoint,mountOpts,optionalFields,optFieldSeparator,fsType,mountSource,superOpts /proc/self/mountinfo | grep -E 'mountID|shm'; sleep 1; done
mountID parentID major:minor rootMount mountPoint mountOpts optionalFields optFieldSeparator fsType mountSource superOpts
32 26 0:27 / /dev/shm rw,nosuid,nodev shared:4 - tmpfs tmpfs rw,inode64
32 26 0:27 / /dev/shm rw,nosuid,nodev shared:4 - tmpfs tmpfs rw,inode64
32 26 0:27 / /dev/shm rw,nosuid,nodev shared:4 - tmpfs tmpfs rw,size=4011076k,nr_inodes=1002769,inode64
32 26 0:27 / /dev/shm rw,nosuid,nodev shared:4 - tmpfs tmpfs rw,size=4011076k,nr_inodes=1002769,inode64
32 26 0:27 / /dev/shm rw,nosuid,nodev shared:4 - tmpfs tmpfs rw,size=4011076k,nr_inodes=1002769,inode64
32 26 0:27 / /dev/shm rw,nosuid,nodev shared:4 - tmpfs tmpfs rw,size=4011076k,nr_inodes=1002769,inode64
32 26 0:27 / /dev/shm rw,nosuid,nodev shared:4 - tmpfs tmpfs rw,size=4011076k,nr_inodes=1002769,inode64
32 26 0:27 / /dev/shm rw,nosuid,nodev shared:4 - tmpfs tmpfs rw,size=4011076k,nr_inodes=1002769,inode64
32 26 0:27 / /dev/shm rw,nosuid,nodev shared:4 - tmpfs tmpfs rw,size=4011076k,nr_inodes=1002769,inode64
32 26 0:27 / /dev/shm rw,nosuid,nodev shared:4 - tmpfs tmpfs rw,size=4011076k,nr_inodes=1002769,inode64
32 26 0:27 / /dev/shm rw,nosuid,nodev shared:4 - tmpfs tmpfs rw,size=4011076k,nr_inodes=1002769,inode64
32 26 0:27 / /dev/shm rw,nosuid,nodev shared:4 - tmpfs tmpfs rw,size=4011076k,nr_inodes=1002769,inode64
32 26 0:27 / /dev/shm rw,nosuid,nodev shared:4 - tmpfs tmpfs rw,inode64
32 26 0:27 / /dev/shm rw,nosuid,nodev shared:4 - tmpfs tmpfs rw,inode64
32 26 0:27 / /dev/shm rw,nosuid,nodev shared:4 - tmpfs tmpfs rw,inode64
32 26 0:27 / /dev/shm rw,nosuid,nodev shared:4 - tmpfs tmpfs rw,inode64
32 26 0:27 / /dev/shm rw,nosuid,nodev shared:4 - tmpfs tmpfs rw,inode64
32 26 0:27 / /dev/shm rw,nosuid,nodev shared:4 - tmpfs tmpfs rw,inode64
32 26 0:27 / /dev/shm rw,nosuid,nodev shared:4 - tmpfs tmpfs rw,inode64
32 26 0:27 / /dev/shm rw,nosuid,nodev shared:4 - tmpfs tmpfs rw,inode64
32 26 0:27 / /dev/shm rw,nosuid,nodev shared:4 - tmpfs tmpfs rw,inode64
32 26 0:27 / /dev/shm rw,nosuid,nodev shared:4 - tmpfs tmpfs rw,size=4011076k,nr_inodes=1002769,inode64
32 26 0:27 / /dev/shm rw,nosuid,nodev shared:4 - tmpfs tmpfs rw,size=4011076k,nr_inodes=1002769,inode64
32 26 0:27 / /dev/shm rw,nosuid,nodev shared:4 - tmpfs tmpfs rw,size=4011076k,nr_inodes=1002769,inode64
32 26 0:27 / /dev/shm rw,nosuid,nodev shared:4 - tmpfs tmpfs rw,size=4011076k,nr_inodes=1002769,inode64
32 26 0:27 / /dev/shm rw,nosuid,nodev shared:4 - tmpfs tmpfs rw,size=4011076k,nr_inodes=1002769,inode64
32 26 0:27 / /dev/shm rw,nosuid,nodev shared:4 - tmpfs tmpfs rw,size=4011076k,nr_inodes=1002769,inode64
32 26 0:27 / /dev/shm rw,nosuid,nodev shared:4 - tmpfs tmpfs rw,size=4011076k,nr_inodes=1002769,inode64
32 26 0:27 / /dev/shm rw,nosuid,nodev shared:4 - tmpfs tmpfs rw,size=4011076k,nr_inodes=1002769,inode64
32 26 0:27 / /dev/shm rw,nosuid,nodev shared:4 - tmpfs tmpfs rw,size=4011076k,nr_inodes=1002769,inode64
32 26 0:27 / /dev/shm rw,nosuid,nodev shared:4 - tmpfs tmpfs rw,size=4011076k,nr_inodes=1002769,inode64
32 26 0:27 / /dev/shm rw,nosuid,nodev shared:4 - tmpfs tmpfs rw,inode64
32 26 0:27 / /dev/shm rw,nosuid,nodev shared:4 - tmpfs tmpfs rw,inode64
32 26 0:27 / /dev/shm rw,nosuid,nodev shared:4 - tmpfs tmpfs rw,inode64
32 26 0:27 / /dev/shm rw,nosuid,nodev shared:4 - tmpfs tmpfs rw,inode64
32 26 0:27 / /dev/shm rw,nosuid,nodev shared:4 - tmpfs tmpfs rw,inode64
32 26 0:27 / /dev/shm rw,nosuid,nodev shared:4 - tmpfs tmpfs rw,inode64
32 26 0:27 / /dev/shm rw,nosuid,nodev shared:4 - tmpfs tmpfs rw,inode64
32 26 0:27 / /dev/shm rw,nosuid,nodev shared:4 - tmpfs tmpfs rw,inode64
32 26 0:27 / /dev/shm rw,nosuid,nodev shared:4 - tmpfs tmpfs rw,inode64
32 26 0:27 / /dev/shm rw,nosuid,nodev shared:4 - tmpfs tmpfs rw,size=4011076k,nr_inodes=1002769,inode64
32 26 0:27 / /dev/shm rw,nosuid,nodev shared:4 - tmpfs tmpfs rw,size=4011076k,nr_inodes=1002769,inode64
32 26 0:27 / /dev/shm rw,nosuid,nodev shared:4 - tmpfs tmpfs rw,size=4011076k,nr_inodes=1002769,inode64
32 26 0:27 / /dev/shm rw,nosuid,nodev shared:4 - tmpfs tmpfs rw,size=4011076k,nr_inodes=1002769,inode64
32 26 0:27 / /dev/shm rw,nosuid,nodev shared:4 - tmpfs tmpfs rw,size=4011076k,nr_inodes=1002769,inode64
32 26 0:27 / /dev/shm rw,nosuid,nodev shared:4 - tmpfs tmpfs rw,size=4011076k,nr_inodes=1002769,inode64
32 26 0:27 / /dev/shm rw,nosuid,nodev shared:4 - tmpfs tmpfs rw,size=4011076k,nr_inodes=1002769,inode64
32 26 0:27 / /dev/shm rw,nosuid,nodev shared:4 - tmpfs tmpfs rw,size=4011076k,nr_inodes=1002769,inode64
32 26 0:27 / /dev/shm rw,nosuid,nodev shared:4 - tmpfs tmpfs rw,size=4011076k,nr_inodes=1002769,inode64
32 26 0:27 / /dev/shm rw,nosuid,nodev shared:4 - tmpfs tmpfs rw,size=4011076k,nr_inodes=1002769,inode64
32 26 0:27 / /dev/shm rw,nosuid,nodev shared:4 - tmpfs tmpfs rw,size=4011076k,nr_inodes=1002769,inode64
32 26 0:27 / /dev/shm rw,nosuid,nodev shared:4 - tmpfs tmpfs rw,inode64
32 26 0:27 / /dev/shm rw,nosuid,nodev shared:4 - tmpfs tmpfs rw,inode64
32 26 0:27 / /dev/shm rw,nosuid,nodev shared:4 - tmpfs tmpfs rw,inode64
32 26 0:27 / /dev/shm rw,nosuid,nodev shared:4 - tmpfs tmpfs rw,inode64
32 26 0:27 / /dev/shm rw,nosuid,nodev shared:4 - tmpfs tmpfs rw,inode64
32 26 0:27 / /dev/shm rw,nosuid,nodev shared:4 - tmpfs tmpfs rw,inode64
32 26 0:27 / /dev/shm rw,nosuid,nodev shared:4 - tmpfs tmpfs rw,inode64
32 26 0:27 / /dev/shm rw,nosuid,nodev shared:4 - tmpfs tmpfs rw,inode64
32 26 0:27 / /dev/shm rw,nosuid,nodev shared:4 - tmpfs tmpfs rw,inode64
32 26 0:27 / /dev/shm rw,nosuid,nodev shared:4 - tmpfs tmpfs rw,inode64
32 26 0:27 / /dev/shm rw,nosuid,nodev shared:4 - tmpfs tmpfs rw,size=4011076k,nr_inodes=1002769,inode64
32 26 0:27 / /dev/shm rw,nosuid,nodev shared:4 - tmpfs tmpfs rw,size=4011076k,nr_inodes=1002769,inode64
32 26 0:27 / /dev/shm rw,nosuid,nodev shared:4 - tmpfs tmpfs rw,size=4011076k,nr_inodes=1002769,inode64
I've tried checking dmesg -wH, using strace (though I do not remember the parameters anymore) on pid 1 (not sure if this is sane or not - ChatGPT suggestion), checking journalctl -k -f and even finding all files on the system and executing grep -IHn '/dev/shm' without finding anything useful. There was a couple of mentions of apparmor, although I disabled that service and it still got remounted.
I compared this to another system running the same version of Ubuntu (although with a slightly different version of the kernel - 6.8.0-63 vs 6.8.0-71) and the issue do not happen there.
How do I troubleshoot this?
forkstatorextraceto see if something is spawning the 'mount' command?