1.\" 2.\" Copyright (c) 1995 David Hovemeyer <[email protected]> 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 1.14 2002/12/19 09:40:25 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 SYNOPSIS 35.In sys/sem.h 36.Ft int 37.Fo semget 38.Fa "key_t key" 39.Fa "int nsems" 40.Fa "int semflg" 41.Fc 42.Sh DESCRIPTION 43Based on the values of 44.Fa key 45and 46.Fa semflg , 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 semflg , 67a new one will be created. 68.It 69The 70.Xr ftok 3 71function 72may be used to generate a key from a pathname. 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 semflg 82argument: 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 105The 106.Fn semget 107system call 108returns the id of a semaphore set if successful; otherwise, -1 109is returned and 110.Va errno 111is set to indicate the error. 112.Sh ERRORS 113The 114.Fn semget 115system call 116will fail if: 117.Bl -tag -width Er 118.\" =========== 119.\" ipcperm could fail (we're opening to read and write, as it were) 120.It Bq Er EACCES 121Access permission failure. 122.\" =========== 123.\" 124.\" sysv_sem.c is quite explicit about these, 125.\" so I'm pretty sure this is accurate 126.\" 127.It Bq Er EEXIST 128IPC_CREAT and IPC_EXCL were specified, 129and a semaphore set corresponding to 130.Fa key 131already exists. 132.\" =========== 133.It Bq Er EINVAL 134The number of semaphores requested 135is either less than 1 or greater than the system imposed maximum per set. 136.\" =========== 137.It Bq Er EINVAL 138A semaphore identifier exists for the argument key, 139but the number of semaphores in the set associated with it 140is less than 141.Fa nsems , 142and 143.Fa nsems 144is non-zero. 145.\" =========== 146.It Bq Er ENOENT 147No semaphore set was found corresponding to 148.Fa key , 149and IPC_CREAT was not specified. 150.\" =========== 151.It Bq Er ENOSPC 152Insufficiently many semaphores are available. 153.\" =========== 154.It Bq Er ENOSPC 155The kernel could not allocate a 156.Fa "struct semid_ds" . 157.El 158.Sh LEGACY SYNOPSIS 159.Fd #include <sys/types.h> 160.Fd #include <sys/ipc.h> 161.Fd #include <sys/sem.h> 162.Pp 163The include files 164.In sys/types.h 165and 166.In sys/ipc.h 167are necessary. 168.Sh SEE ALSO 169.Xr semctl 2 , 170.Xr semop 2 , 171.Xr ftok 3 , 172.Xr compat 5 173