1.\" 2.\" Copyright (c) 1995 David Hovemeyer <daveho@infocom.com> 3.\" 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.\" 15.\" THIS SOFTWARE IS PROVIDED BY THE DEVELOPERS ``AS IS'' AND ANY EXPRESS OR 16.\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES 17.\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. 18.\" IN NO EVENT SHALL THE DEVELOPERS BE LIABLE FOR ANY DIRECT, INDIRECT, 19.\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT 20.\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, 21.\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY 22.\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT 23.\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF 24.\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 25.\" 26.\" $FreeBSD: src/lib/libc/sys/semget.2,v 1.7.2.5 2001/12/14 18:34:01 ru Exp $ 27.\" 28.Dd January 4, 2014 29.Dt SEMGET 2 30.Os 31.Sh NAME 32.Nm semget 33.Nd obtain a semaphore id 34.Sh LIBRARY 35.Lb libc 36.Sh SYNOPSIS 37.In sys/types.h 38.In sys/ipc.h 39.In sys/sem.h 40.Ft int 41.Fn semget "key_t key" "int nsems" "int flag" 42.Sh DESCRIPTION 43Based on the values of 44.Fa key 45and 46.Fa flag , 47.Fn semget 48returns the identifier of a newly created or previously existing 49set of semaphores. 50.\" 51.\" This is copied verbatim from the shmget manpage. Perhaps 52.\" it should go in a common manpage, such as .Xr ipc 2 53.\" 54The key 55is analogous to a filename: it provides a handle that names an 56IPC object. 57There are three ways to specify a key: 58.Bl -bullet 59.It 60.Dv IPC_PRIVATE 61may be specified, in which case a new IPC object will be created. 62.It 63An integer constant may be specified. 64If no IPC object corresponding to 65.Fa key 66is specified and the 67.Dv IPC_CREAT 68bit is set in 69.Fa flag , 70a new one will be created. 71.It 72.Fn ftok 73may be used to generate a key from a pathname. 74See 75.Xr ftok 3 . 76.El 77.\" 78.\" Likewise for this section, except SHM_* becomes SEM_*. 79.\" 80.Pp 81The mode of a newly created IPC object is determined by 82.Em OR Ns 'ing 83the following constants into the 84.Fa flag 85parameter: 86.Bl -tag -width XSEM_WXX6XXX 87.It Dv SEM_R 88Read access for user. 89.It Dv SEM_A 90Alter access for user. 91.It Dv ( SEM_R>>3 ) 92Read access for group. 93.It Dv ( SEM_A>>3 ) 94Alter access for group. 95.It Dv ( SEM_R>>6 ) 96Read access for other. 97.It Dv ( SEM_A>>6 ) 98Alter access for other. 99.El 100.Pp 101If a new set of semaphores is being created, 102.Fa nsems 103is used to indicate the number of semaphores the set should contain. 104Otherwise, 105.Fa nsems 106may be specified as 0. 107.Sh RETURN VALUES 108.Fn Semget 109returns the id of a semaphore set if successful; otherwise, -1 110is returned and 111.Va errno 112is set to indicate the error. 113.Sh ENVIRONMENT 114The XSI Interprocess Communication family of functions is also available 115as an implementation in userspace. 116To use it, the 117.Xr sysvipcd 8 118daemon has to be running. 119.Pp 120If the 121.Ev USR_SYSVIPC 122variable is set in a process' environment, the process and its children 123will use the userspace implementation. 124.Sh ERRORS 125.Fn Semget 126will fail if: 127.Bl -tag -width Er 128.\" ipcperm could fail (we're opening to read and write, as it were) 129.It Bq Er EACCES 130Access permission failure. 131.\" 132.\" sysv_sem.c is quite explicit about these, so I'm pretty sure 133.\" this is accurate 134.\" 135.It Bq Er EEXIST 136.Dv IPC_CREAT 137and 138.Dv IPC_EXCL 139were specified, and a semaphore set corresponding to 140.Fa key 141already exists. 142.It Bq Er EINVAL 143The number of semaphores requested exceeds the system imposed maximum 144per set. 145.It Bq Er ENOSPC 146Insufficiently many semaphores are available. 147.It Bq Er ENOSPC 148The kernel could not allocate a 149.Fa "struct semid_ds" . 150.It Bq Er ENOENT 151No semaphore set was found corresponding to 152.Fa key , 153and 154.Dv IPC_CREAT 155was not specified. 156.El 157.Sh SEE ALSO 158.Xr semctl 2 , 159.Xr semop 2 , 160.Xr ftok 3 161