1.\" $NetBSD: semget.2,v 1.18 2006/10/08 08:22:34 rillig Exp $ 2.\" 3.\" Copyright (c) 1995 Frank van der Linden 4.\" All rights reserved. 5.\" 6.\" Redistribution and use in source and binary forms, with or without 7.\" modification, are permitted provided that the following conditions 8.\" are met: 9.\" 1. Redistributions of source code must retain the above copyright 10.\" notice, this list of conditions and the following disclaimer. 11.\" 2. Redistributions in binary form must reproduce the above copyright 12.\" notice, this list of conditions and the following disclaimer in the 13.\" documentation and/or other materials provided with the distribution. 14.\" 3. All advertising materials mentioning features or use of this software 15.\" must display the following acknowledgement: 16.\" This product includes software developed for the NetBSD Project 17.\" by Frank van der Linden 18.\" 4. The name of the author may not be used to endorse or promote products 19.\" derived from this software without specific prior written permission 20.\" 21.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR 22.\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES 23.\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. 24.\" IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, 25.\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT 26.\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, 27.\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY 28.\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT 29.\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF 30.\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 31.\" 32.Dd May 13, 2004 33.Dt SEMGET 2 34.Os 35.Sh NAME 36.Nm semget 37.Nd get set of semaphores 38.Sh LIBRARY 39.Lb libc 40.Sh SYNOPSIS 41.In sys/sem.h 42.Ft int 43.Fn semget "key_t key" "int nsems" "int semflg" 44.Sh DESCRIPTION 45The 46.Fn semget 47system call returns the semaphore identifier associated with 48.Fa key . 49.Pp 50A new set containing 51.Fa nsems 52semaphores is created if either 53.Fa key 54is equal to 55.Dv IPC_PRIVATE , 56or 57.Fa key 58does not have a semaphore set associated with it and the 59.Dv IPC_CREAT 60bit is set in 61.Fa semflg . 62If both the 63.Dv IPC_CREAT 64bit and the 65.Dv IPC_EXCL 66bit are set in 67.Fa semflg , 68and 69.Fa key 70has a semaphore set associated with it already, 71the operation will fail. 72.Pp 73If a new set of semaphores is created, the data structure associated with it 74(the 75.Va semid_ds 76structure, see 77.Xr semctl 2 ) 78is initialized as follows: 79.Bl -bullet 80.It 81.Va sem_perm.cuid 82and 83.Va sem_perm.uid 84are set to the effective uid of the calling process. 85.It 86.Va sem_perm.gid 87and 88.Va sem_perm.cgid 89are set to the effective gid of the calling process. 90.It 91.Va sem_perm.mode 92is set to the lower 9 bits of 93.Fa semflg . 94.It 95.Va sem_nsems 96is set to the value of 97.Fa nsems . 98.It 99.Va sem_ctime 100is set to the current time. 101.It 102.Va sem_otime 103is set to 0. 104.El 105.Sh RETURN VALUES 106.Fn semget 107returns a non-negative semaphore identifier if successful. 108Otherwise, \-1 is returned and 109.Va errno 110is set to reflect the error. 111.Sh ERRORS 112.Bl -tag -width Er 113.It Bq Er EACCES 114The caller has no permission to access a semaphore set already associated with 115.Fa key . 116.It Bq Er EEXIST 117Both 118.Dv IPC_CREAT 119and 120.Dv IPC_EXCL 121are set in 122.Fa semflg , 123and a semaphore set is already associated with 124.Fa key . 125.It Bq Er EINVAL 126.Va nsems 127is less than 0 or greater than the system limit for the number in a semaphore 128set. 129.Pp 130A semaphore set associated with 131.Fa key 132exists, but has fewer semaphores than the number specified in 133.Fa nsems . 134.It Bq Er ENOSPC 135A new set of semaphores could not be created because the system limit 136for the number of semaphores or the number of semaphore sets has been 137reached. 138.It Bq Er ENOENT 139.Dv IPC_CREAT 140is not set in 141.Fa semflg 142and no semaphore set associated with 143.Fa key 144was found. 145.El 146.Sh SEE ALSO 147.Xr ipcs 1 , 148.Xr semctl 2 , 149.Xr semop 2 , 150.Xr ftok 3 151.Sh STANDARDS 152The 153.Nm 154system call conforms to 155.St -xsh5 . 156.Sh HISTORY 157Semaphores appeared in the first release of 158.At V . 159