1.\" $OpenBSD: semget.2,v 1.18 2014/02/13 07:30:39 guenther Exp $ 2.\" $NetBSD: semget.2,v 1.2 1997/03/27 08:20:41 mikel Exp $ 3.\" 4.\" Copyright (c) 1995 Frank van der Linden 5.\" All rights reserved. 6.\" 7.\" Redistribution and use in source and binary forms, with or without 8.\" modification, are permitted provided that the following conditions 9.\" are met: 10.\" 1. Redistributions of source code must retain the above copyright 11.\" notice, this list of conditions and the following disclaimer. 12.\" 2. Redistributions in binary form must reproduce the above copyright 13.\" notice, this list of conditions and the following disclaimer in the 14.\" documentation and/or other materials provided with the distribution. 15.\" 3. All advertising materials mentioning features or use of this software 16.\" must display the following acknowledgement: 17.\" This product includes software developed for the NetBSD Project 18.\" by Frank van der Linden 19.\" 4. The name of the author may not be used to endorse or promote products 20.\" derived from this software without specific prior written permission 21.\" 22.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR 23.\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES 24.\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. 25.\" IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, 26.\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT 27.\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, 28.\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY 29.\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT 30.\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF 31.\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 32.\"/ 33.Dd $Mdocdate: February 13 2014 $ 34.Dt SEMGET 2 35.Os 36.Sh NAME 37.Nm semget 38.Nd get semaphore set 39.Sh SYNOPSIS 40.Fd #include <sys/types.h> 41.Fd #include <sys/ipc.h> 42.Fd #include <sys/sem.h> 43.Ft int 44.Fn semget "key_t key" "int nsems" "int semflg" 45.Sh DESCRIPTION 46The 47.Fn semget 48system call returns the semaphore identifier associated with 49.Fa key . 50.Pp 51A new set containing 52.Fa nsems 53semaphores is created if either 54.Fa key 55is equal to 56.Dv IPC_PRIVATE , 57or 58.Fa key 59does not have a semaphore set associated with it and the 60.Dv IPC_CREAT 61bit is set in 62.Fa semflg . 63.Pp 64The access modes of the created semaphores is specified in 65.Fa semflg 66as a bitwise OR of zero or more of the following values: 67.Bd -literal -offset indent 68SEM_A alter permission for owner 69SEM_R read permission for owner 70 71SEM_A >> 3 alter permission for group 72SEM_R >> 3 read permission for group 73 74SEM_A >> 6 alter permission for other 75SEM_R >> 6 read permission for other 76.Ed 77.Pp 78If a new set of semaphores is created, the data structure associated with it 79(the 80.Va semid_ds 81structure, see 82.Xr semctl 2 ) 83is initialized as follows: 84.Bl -bullet 85.It 86.Va sem_perm.cuid 87and 88.Va sem_perm.uid 89are set to the effective UID of the calling process. 90.It 91.Va sem_perm.gid 92and 93.Va sem_perm.cgid 94are set to the effective GID of the calling process. 95.It 96.Va sem_perm.mode 97is set to the lower 9 bits of 98.Fa semflg . 99.It 100.Va sem_nsems 101is set to the value of 102.Fa nsems . 103.It 104.Va sem_ctime 105is set to the current time. 106.It 107.Va sem_otime 108is set to 0. 109.El 110.Sh RETURN VALUES 111.Fn semget 112returns a non-negative semaphore identifier if successful. 113Otherwise, \-1 is returned and 114.Va errno 115is set to reflect the error. 116.Sh ERRORS 117.Bl -tag -width Er 118.It Bq Er EACCES 119The caller has no permission to access a semaphore set already associated with 120.Fa key . 121.It Bq Er EEXIST 122Both 123.Dv IPC_CREAT 124and 125.Dv IPC_EXCL 126are set in 127.Fa semflg , 128and a semaphore set is already associated with 129.Fa key . 130.It Bq Er EINVAL 131.Va nsems 132is less than or equal to 0 or greater than the system limit for the 133number in a semaphore set. 134.Pp 135A semaphore set associated with 136.Fa key 137exists, but has fewer semaphores than the number specified in 138.Fa nsems . 139.It Bq Er ENOSPC 140A new set of semaphores could not be created because the system limit 141for the number of semaphores or the number of semaphore sets has been 142reached. 143.It Bq Er ENOENT 144.Dv IPC_CREAT 145was not set in 146.Fa semflg 147and no semaphore set associated with 148.Fa key 149was found. 150.El 151.Sh SEE ALSO 152.Xr semctl 2 , 153.Xr semop 2 , 154.Xr ftok 3 155