.\" $OpenBSD: semget.2,v 1.17 2007/05/31 19:19:33 jmc Exp $ .\" $NetBSD: semget.2,v 1.2 1997/03/27 08:20:41 mikel Exp $ .\" .\" Copyright (c) 1995 Frank van der Linden .\" All rights reserved. .\" .\" Redistribution and use in source and binary forms, with or without .\" modification, are permitted provided that the following conditions .\" are met: .\" 1. Redistributions of source code must retain the above copyright .\" notice, this list of conditions and the following disclaimer. .\" 2. Redistributions in binary form must reproduce the above copyright .\" notice, this list of conditions and the following disclaimer in the .\" documentation and/or other materials provided with the distribution. .\" 3. All advertising materials mentioning features or use of this software .\" must display the following acknowledgement: .\" This product includes software developed for the NetBSD Project .\" by Frank van der Linden .\" 4. The name of the author may not be used to endorse or promote products .\" derived from this software without specific prior written permission .\" .\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR .\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES .\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. .\" IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, .\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT .\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, .\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY .\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT .\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF .\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. .\"/ .Dd $Mdocdate: May 31 2007 $ .Dt SEMGET 2 .Os .Sh NAME .Nm semget .Nd get semaphore set .Sh SYNOPSIS .Fd #include <sys/types.h> .Fd #include <sys/ipc.h> .Fd #include <sys/sem.h> .Ft int .Fn semget "key_t key" "int nsems" "int semflg" .Sh DESCRIPTION The .Fn semget system call returns the semaphore identifier associated with .Fa key . .Pp A new set containing .Fa nsems semaphores is created if either .Fa key is equal to .Dv IPC_PRIVATE , or .Fa key does not have a semaphore set associated with it and the .Dv IPC_CREAT bit is set in .Fa semflg . .Pp The access modes of the created semaphores is specified in .Fa semflg by .Tn OR Ns 'ing the following values: .Bd -literal -offset indent SEM_A alter permission for owner SEM_R read permission for owner SEM_A >> 3 alter permission for group SEM_R >> 3 read permission for group SEM_A >> 6 alter permission for other SEM_R >> 6 read permission for other .Ed .Pp If a new set of semaphores is created, the data structure associated with it (the .Va semid_ds structure, see .Xr semctl 2 ) is initialized as follows: .Bl -bullet .It .Va sem_perm.cuid and .Va sem_perm.uid are set to the effective UID of the calling process. .It .Va sem_perm.gid and .Va sem_perm.cgid are set to the effective GID of the calling process. .It .Va sem_perm.mode is set to the lower 9 bits of .Fa semflg . .It .Va sem_nsems is set to the value of .Fa nsems . .It .Va sem_ctime is set to the current time. .It .Va sem_otime is set to 0. .El .Sh RETURN VALUES .Fn semget returns a non-negative semaphore identifier if successful. Otherwise, \-1 is returned and .Va errno is set to reflect the error. .Sh ERRORS .Bl -tag -width Er .It Bq Er EACCES The caller has no permission to access a semaphore set already associated with .Fa key . .It Bq Er EEXIST Both .Dv IPC_CREAT and .Dv IPC_EXCL are set in .Fa semflg , and a semaphore set is already associated with .Fa key . .It Bq Er EINVAL .Va nsems is less than or equal to 0 or greater than the system limit for the number in a semaphore set. .Pp A semaphore set associated with .Fa key exists, but has fewer semaphores than the number specified in .Fa nsems . .It Bq Er ENOSPC A new set of semaphores could not be created because the system limit for the number of semaphores or the number of semaphore sets has been reached. .It Bq Er ENOENT .Dv IPC_CREAT was not set in .Fa semflg and no semaphore set associated with .Fa key was found. .El .Sh SEE ALSO .Xr semctl 2 , .Xr semop 2 , .Xr ftok 3