A lock is a software security feature for the application to run correctly.
If a lock is not set, the literal ### displays in the location.
If a lock is set, the port number of the process holding the lock is displayed by the list-locks command.
| fq | Form queue lock is locked whenever a form queue is attached to a printer. |
| iq | Input queue lock indicates the maximum number of jobs that may be open at once. The limit is about 650 permanent (hold-type) entries. |
| mq | Master queue lock is locked by the spooler process when altering any of its tables, such as when a printer is being started. |
| peq | Printer element queue lock is locked briefly by each user as the first byte of a spooler entry is produced. |