159 lines
4 KiB
Groff
159 lines
4 KiB
Groff
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.\" $NetBSD: semget.2,v 1.18 2006/10/08 08:22:34 rillig Exp $
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.\"
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.\" Copyright (c) 1995 Frank van der Linden
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.\" All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\" 3. All advertising materials mentioning features or use of this software
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.\" must display the following acknowledgement:
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.\" This product includes software developed for the NetBSD Project
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.\" by Frank van der Linden
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.\" 4. The name of the author may not be used to endorse or promote products
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.\" derived from this software without specific prior written permission
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
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.\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
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.\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
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.\" IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
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.\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
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.\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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.\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
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.\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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.\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
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.\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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.\"
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.Dd May 13, 2004
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.Dt SEMGET 2
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.Os
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.Sh NAME
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.Nm semget
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.Nd get set of semaphores
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.Sh LIBRARY
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.Lb libc
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.Sh SYNOPSIS
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.In sys/sem.h
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.Ft int
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.Fn semget "key_t key" "int nsems" "int semflg"
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.Sh DESCRIPTION
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The
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.Fn semget
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system call returns the semaphore identifier associated with
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.Fa key .
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.Pp
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A new set containing
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.Fa nsems
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semaphores is created if either
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.Fa key
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is equal to
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.Dv IPC_PRIVATE ,
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or
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.Fa key
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does not have a semaphore set associated with it and the
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.Dv IPC_CREAT
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bit is set in
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.Fa semflg .
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If both the
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.Dv IPC_CREAT
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bit and the
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.Dv IPC_EXCL
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bit are set in
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.Fa semflg ,
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and
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.Fa key
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has a semaphore set associated with it already,
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the operation will fail.
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.Pp
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If a new set of semaphores is created, the data structure associated with it
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(the
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.Va semid_ds
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structure, see
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.Xr semctl 2 )
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is initialized as follows:
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.Bl -bullet
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.It
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.Va sem_perm.cuid
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and
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.Va sem_perm.uid
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are set to the effective uid of the calling process.
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.It
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.Va sem_perm.gid
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and
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.Va sem_perm.cgid
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are set to the effective gid of the calling process.
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.It
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.Va sem_perm.mode
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is set to the lower 9 bits of
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.Fa semflg .
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.It
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.Va sem_nsems
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is set to the value of
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.Fa nsems .
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.It
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.Va sem_ctime
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is set to the current time.
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.It
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.Va sem_otime
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is set to 0.
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.El
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.Sh RETURN VALUES
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.Fn semget
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returns a non-negative semaphore identifier if successful.
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Otherwise, \-1 is returned and
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.Va errno
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is set to reflect the error.
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.Sh ERRORS
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.Bl -tag -width Er
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.It Bq Er EACCES
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The caller has no permission to access a semaphore set already associated with
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.Fa key .
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.It Bq Er EEXIST
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Both
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.Dv IPC_CREAT
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and
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.Dv IPC_EXCL
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are set in
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.Fa semflg ,
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and a semaphore set is already associated with
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.Fa key .
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.It Bq Er EINVAL
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.Va nsems
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is less than 0 or greater than the system limit for the number in a semaphore
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set.
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.Pp
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A semaphore set associated with
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.Fa key
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exists, but has fewer semaphores than the number specified in
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.Fa nsems .
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.It Bq Er ENOSPC
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A new set of semaphores could not be created because the system limit
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for the number of semaphores or the number of semaphore sets has been
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reached.
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.It Bq Er ENOENT
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.Dv IPC_CREAT
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is not set in
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.Fa semflg
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and no semaphore set associated with
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.Fa key
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was found.
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.El
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.Sh SEE ALSO
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.Xr ipcs 1 ,
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.Xr semctl 2 ,
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.Xr semop 2 ,
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.Xr ftok 3
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.Sh STANDARDS
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The
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.Nm
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system call conforms to
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.St -xsh5 .
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.Sh HISTORY
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Semaphores appeared in the first release of
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.At V .
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