# Locks (Spooler)

A lock is a software security feature for the application to run correctly.

There are four locks specifically associated with the spooler:

- Form

- Input

- Master

- Printer element (or entry)

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. |

## See also

- [list-locks command](https://d3codex.com/tcl/list-locks-command/)
- [what command](https://d3codex.com/tcl/what-command/)

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Source: https://d3codex.com/tcl/locks-spooler/ - part of the D3Codex reference.