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.\" $DragonFly: src/lib/libc/sys/semget.2,v 1.2 2003/06/17 04:26:47 dillon Exp $ 28.\" 29.Dd September 12, 1995 30.Dt SEMGET 2 31.Os 32.Sh NAME 33.Nm semget 34.Nd obtain a semaphore id 35.Sh LIBRARY 36.Lb libc 37.Sh SYNOPSIS 38.In sys/types.h 39.In sys/ipc.h 40.In sys/sem.h 41.Ft int 42.Fn semget "key_t key" "int nsems" "int flag" 43.Sh DESCRIPTION 44Based on the values of 45.Fa key 46and 47.Fa flag , 48.Fn semget 49returns the identifier of a newly created or previously existing 50set of semaphores. 51.\" 52.\" This is copied verbatim from the shmget manpage. Perhaps 53.\" it should go in a common manpage, such as .Xr ipc 2 54.\" 55The key 56is analogous to a filename: it provides a handle that names an 57IPC object. There are three ways to specify a key: 58.Bl -bullet 59.It 60IPC_PRIVATE may be specified, in which case a new IPC object 61will be created. 62.It 63An integer constant may be specified. If no IPC object corresponding 64to 65.Fa key 66is specified and the IPC_CREAT bit is set in 67.Fa flag , 68a new one will be created. 69.It 70.Fn ftok 71may be used to generate a key from a pathname. See 72.Xr ftok 3 . 73.El 74.\" 75.\" Likewise for this section, except SHM_* becomes SEM_*. 76.\" 77.Pp 78The mode of a newly created IPC object is determined by 79.Em OR Ns 'ing 80the following constants into the 81.Fa flag 82parameter: 83.Bl -tag -width XSEM_WXX6XXX 84.It Dv SEM_R 85Read access for user. 86.It Dv SEM_A 87Alter access for user. 88.It Dv ( SEM_R>>3 ) 89Read access for group. 90.It Dv ( SEM_A>>3 ) 91Alter access for group. 92.It Dv ( SEM_R>>6 ) 93Read access for other. 94.It Dv ( SEM_A>>6 ) 95Alter access for other. 96.El 97.Pp 98If a new set of semaphores is being created, 99.Fa nsems 100is used to indicate the number of semaphores the set should contain. 101Otherwise, 102.Fa nsems 103may be specified as 0. 104.Sh RETURN VALUES 105.Fn Semget 106returns the id of a semaphore set if successful; otherwise, -1 107is returned and 108.Va errno 109is set to indicate the error. 110.Sh ERRORS 111.Fn Semget 112will fail if: 113.Bl -tag -width Er 114.\" ipcperm could fail (we're opening to read and write, as it were) 115.It Bq Er EACCES 116Access permission failure. 117.\" 118.\" sysv_sem.c is quite explicit about these, so I'm pretty sure 119.\" this is accurate 120.\" 121.It Bq Er EEXIST 122IPC_CREAT and IPC_EXCL were specified, and a semaphore set 123corresponding to 124.Fa key 125already exists. 126.It Bq Er EINVAL 127The number of semaphores requested exceeds the system imposed maximum 128per set. 129.It Bq Er ENOSPC 130Insufficiently many semaphores are available. 131.It Bq Er ENOSPC 132The kernel could not allocate a 133.Fa "struct semid_ds" . 134.It Bq Er ENOENT 135No semaphore set was found corresponding to 136.Fa key , 137and IPC_CREAT was not specified. 138.El 139.Sh SEE ALSO 140.Xr semctl 2 , 141.Xr semop 2 , 142.Xr ftok 3 143