I installed R4.0.4 RC1 on a new machine and restored my VM’s from a backup. Somewhere along the way, I started getting “cannot execute qubesdb-daemon” errors and could not start some VM’s that I had not yet run since the restore process.
After a bit of sleuthing, I found that some of the log files in /var/log/qubes/qubesdb. .log had the ownership of root.qubes rather than .qubes. Once I did a chown to correct this problem everything was back up and running.
I don’t know how these logs got the root ownership applied to them, but when the logfile could not be opened in the current user context from the menu, qubes panel, or qvm-run command, the qubesdb-daemon was just quitting without being able to log anything. The popup message was the only feedback information to go by for chasing this down to the source of the error. While this isn’t a big deal for me it might be wise to do a permissions check and a more useful message on failure since there is no logfile at that point.