What would cause SQL one or multiple databases to switch to single-user mode?

Question

Have over 25 databases throughout our organization. Over the weekend 7 of them automatically switched to single-user mode. We have no idea why. We were able to switch them back, but were confused as to why they jumped from multi-user mode randomly.

There may be 2 catalysts: 1. Hard drive ran out of free space. Backups and transaction logs being backed up to same drive, caused it to run out of free space.

1. Ran Shrink Database script on 3 of those 7 databases hours before the incidents.

Have checked event logs, but only errors it shows for that day is the "out of space" issue.

Any input would be appreciated.

Answer 1

DBCC CHECKDB put the database into single user mode. So it is possible that repair porcess was started on it (automatically or not) and was hanged.