"failed to mount Mount unit for <program>" when restarting the system

When I restart my Ubuntu 18.04 system, it suddenly crashes and shows a long list of [FAILED] messages as shown above, for example:

[FAILED] Failed to mount Mount unit for gtk-common-themes, revision 1198
See 'systemctl status "snap-gtk\\x2dcommon\\x2dthemes-1198.mount"' for details

and other mount errors like

[FAILED] Failed to mount FUSE Control File System

What could be the problem here, and how can I fix it?

Solution 1:

If you deleted snap files manually, for instance, in order to clean up space, some .mount files were left in /etc/systemd/system/, like /etc/systemd/system/snap-core20-975.mount.

You can try the following command:

grep -r What /etc/systemd/system/|sed -E 's/.*What=(.*)/\1/g'|xargs ls -la {}

The output will be:

ls: cannot access '/var/lib/snapd/snaps/snap-postman_81.snap': No such file or directory
-rw------- 2 root root  64233472 Mai 19 22:11 /var/lib/snapd/snaps/****.snap
....

So, now you know what snaps are missing and can decide what to do, e.g. remove obsolete .mount files.