You need to restart psql12:
systemctl restart rh-postgresql12-postgresql
Yesterday evening I had a session with @mrmarkuz to solve the problem. It turned out that migrating mattermost from postgresql 9.x to 12.x went wrong. Because this went wrong, the pre-backup script failed. There was no database in the postgresql 12 directory. The script couldnât find the database and exited with the message: âerrorâ
And that was about all the info there was in the backuplog.
This brings me to the suggestion to have a more verbose logging. Maybe only as an extra option, but IMO the reason for logs is to get some clues about what went wrong. A message âerrorâ only gives one clue and that there went something wrong.
To start troubleshooting just a message âerrorâ doesnât help. Is there a way that a more verbose logging for the backup (backup-data) can be activated or at least created?
@filippo_carletti @giacomo @support_team
Every output (stderr or stout) is generated by the script is automatically registered inside /var/log/messages. If the script causing the error was written by us, we can for sure improve the output. 
Otherwise, itâs better to report a bug upstream.