spooler.locks

four locks specifically associated with the spooler: the 'master', 'input', 'form' and 'permanent element (or entry)'.

If a lock is not set, the literal '###' appears in the location.
If a lock is set, the port.number of the process holding the lock is displayed by the 'list-locks' command.

'mq' is the 'master queue' lock. It is locked by the Spooler process when altering any of its tables, such as when a printer is being started.

'iq' is the 'input queue' lock. It indicates the maximum number of jobs that may be open at once. The limit is about 650 'permanent' (hold-type) entries.

'fq' is the 'form queue' lock. It is locked whenever a form queue is attached to a printer.

'peq' is the 'printer element queue' lock. It is locked briefly by each user as the first byte of a Spooler entry is produced.