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Full Discussion: file descriptors
Top Forums UNIX for Dummies Questions & Answers file descriptors Post 46836 by fpmurphy on Tuesday 27th of January 2004 06:46:14 PM
Old 01-27-2004
Note that processes do not have a limit of 20 file descriptors
as suggested in your mail - rather the limit is OPEN_MAX.

Here is the formal POSIX definition of a file descriptor:

A per-process unique, non-negative integer used to identify an open file for the purpose of file access. The value of a file descriptor is from zero to OPEN_MAX. A process can have no more than OPEN_MAX file descriptors open simultaneously.

Note also the difference between file DESCRIPTOR and file DESCRIPTION. From SUSv3 ....

(Open) File Description

A record of how a process or group of processes is accessing a file. Each file descriptor refers to exactly one open file description, but an open file description can be referred to by more than one file descriptor. The file offset, file status, and file access modes are attributes of an open file description.

- Finnbarr
 

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LEARN ABOUT HPUX

pipcrm

pipcrm(1)						      General Commands Manual							 pipcrm(1)

NAME

       pipcrm - remove a POSIX message queue or a POSIX named semaphore

SYNOPSIS

       [option]...

DESCRIPTION

       The command removes one or more specified POSIX message queue or POSIX named semaphore.

   Options
       The identifiers are specified by the following options:

	      Unlinks the queue name from the message queue
			     specified	by the argument, msqname.  If there are no processes with existing open descriptors for the message queue,
			     the queue is destroyed.  If one or more processes have the message queue open, the removal of the queue is  postponed
			     until all descriptors for the queue have been closed.

	      Unlinks the semaphore name from the semaphore
			     specified	by the argument, semname.  If there are no processes with existing open descriptors for the semaphore, the
			     semaphore is destroyed.  If one or more processes have the semaphore open, the removal of the semaphore is  postponed
			     until all descriptors for the semaphore have been closed.

       The details of the removals are described in mq_unlink(2), and sem_unlink(2).  The names can be found by using (see pipcs(1)).

SEE ALSO

       pipcs(1), mq_unlink(2), mq_open(2), mq_send(2), mq_receive(2), sem_unlink(2), sem_open(2), sem_wait(2), sem_post(2).

STANDARDS CONFORMANCE

																	 pipcrm(1)
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