Server service stopped and cannot be restarted

[MrBates]

Ubuntu 18.04.
The server service stopped, and cannot be restarted.

# service urbackupsrv status
● urbackupsrv.service - LSB: Server for doing backups
   Loaded: loaded (/etc/init.d/urbackupsrv; generated)
   Active: active (exited) since Tue 2018-07-31 21:28:28 IDT; 1 weeks 0 days ago
     Docs: man:systemd-sysv-generator(8)
  Process: 26423 ExecStop=/etc/init.d/urbackupsrv stop (code=exited, status=0/SUCCESS)
  Process: 26436 ExecStart=/etc/init.d/urbackupsrv start (code=exited, status=0/SUCCESS)

The log has entries like these:

2018-08-06 20:17:55: ERROR: Cannot read file tree from file "urbackup/clientlist_1.ub"
2018-08-07 03:05:18: ERROR: Backing up database failed. Copying urbackup/backup_server.db-wal to /storage/urbackup/urbackup/backup_server.db-wal~ failed. No such file or directory (code: 2)
2018-08-07 03:05:20: ERROR: Backing up database failed. Copying urbackup/backup_server_settings.db-wal to /storage/urbackup/urbackup/backup_server_settings.db-wal~ failed. No such file or directory (code: 2)
2018-08-07 03:05:41: ERROR: Backing up database failed. Copying urbackup/backup_server_files.db-wal to /storage/urbackup/urbackup/backup_server_files.db-wal~ failed. No such file or directory (code: 2)
2018-08-07 03:05:43: ERROR: Backing up database failed. Copying urbackup/backup_server_links.db-wal to /storage/urbackup/urbackup/backup_server_links.db-wal~ failed. No such file or directory (code: 2)
2018-08-07 03:05:45: ERROR: Backing up database failed. Copying urbackup/backup_server_link_journal.db-wal to /storage/urbackup/urbackup/backup_server_link_journal.db-wal~ failed. No such file or directory (code: 2)

Running remove-unknown also complains:

2018-08-08 10:02:39: Could not open WAL file urbackup/backup_server_files.db-wal (wal checkpoint thread)
2018-08-08 10:02:39: Could not open WAL file urbackup/backup_server_link_journal.db-wal (wal checkpoint thread)
2018-08-08 10:02:39: Could not open WAL file urbackup/backup_server_settings.db-wal (wal checkpoint thread)
2018-08-08 10:02:39: Could not open WAL file urbackup/backup_server.db-wal (wal checkpoint thread)
2018-08-08 10:02:39: Could not open WAL file urbackup/backup_server_links.db-wal (wal checkpoint thread)

Disk has enough free space.

Ideas?

[uroni]

Could you run it in debug mode?

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[MrBates]

As instructed, I changed the log level from warn to debug and restarted the urbackup service.
But no /var/log/urbackup.log was created! (I renamed the old one)

[MrBates]

Restarting the server solved the problem.
No idea what it was…