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 September 12, 1995 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. There are three ways to specify a key: 57.Bl -bullet 58.It 59IPC_PRIVATE may be specified, in which case a new IPC object 60will be created. 61.It 62An integer constant may be specified. If no IPC object corresponding 63to 64.Fa key 65is specified and the IPC_CREAT bit is set in 66.Fa flag , 67a new one will be created. 68.It 69.Fn ftok 70may be used to generate a key from a pathname. See 71.Xr ftok 3 . 72.El 73.\" 74.\" Likewise for this section, except SHM_* becomes SEM_*. 75.\" 76.Pp 77The mode of a newly created IPC object is determined by 78.Em OR Ns 'ing 79the following constants into the 80.Fa flag 81parameter: 82.Bl -tag -width XSEM_WXX6XXX 83.It Dv SEM_R 84Read access for user. 85.It Dv SEM_A 86Alter access for user. 87.It Dv ( SEM_R>>3 ) 88Read access for group. 89.It Dv ( SEM_A>>3 ) 90Alter access for group. 91.It Dv ( SEM_R>>6 ) 92Read access for other. 93.It Dv ( SEM_A>>6 ) 94Alter access for other. 95.El 96.Pp 97If a new set of semaphores is being created, 98.Fa nsems 99is used to indicate the number of semaphores the set should contain. 100Otherwise, 101.Fa nsems 102may be specified as 0. 103.Sh RETURN VALUES 104.Fn Semget 105returns the id of a semaphore set if successful; otherwise, -1 106is returned and 107.Va errno 108is set to indicate the error. 109.Sh ERRORS 110.Fn Semget 111will fail if: 112.Bl -tag -width Er 113.\" ipcperm could fail (we're opening to read and write, as it were) 114.It Bq Er EACCES 115Access permission failure. 116.\" 117.\" sysv_sem.c is quite explicit about these, so I'm pretty sure 118.\" this is accurate 119.\" 120.It Bq Er EEXIST 121IPC_CREAT and IPC_EXCL were specified, and a semaphore set 122corresponding to 123.Fa key 124already exists. 125.It Bq Er EINVAL 126The number of semaphores requested exceeds the system imposed maximum 127per set. 128.It Bq Er ENOSPC 129Insufficiently many semaphores are available. 130.It Bq Er ENOSPC 131The kernel could not allocate a 132.Fa "struct semid_ds" . 133.It Bq Er ENOENT 134No semaphore set was found corresponding to 135.Fa key , 136and IPC_CREAT was not specified. 137.El 138.Sh SEE ALSO 139.Xr semctl 2 , 140.Xr semop 2 , 141.Xr ftok 3 142