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.\" $FreeBSD$ 27.\" 28.Dd March 4, 2018 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/sem.h 38.Ft int 39.Fn semget "key_t key" "int nsems" "int flag" 40.Sh DESCRIPTION 41Based on the values of 42.Fa key 43and 44.Fa flag , 45.Fn semget 46returns the identifier of a newly created or previously existing 47set of semaphores. 48.\" 49.\" This is copied verbatim from the shmget manpage. Perhaps 50.\" it should go in a common manpage, such as .Xr ipc 2 51.\" 52The key 53is analogous to a filename: it provides a handle that names an 54IPC object. 55There are three ways to specify a key: 56.Bl -bullet 57.It 58IPC_PRIVATE may be specified, in which case a new IPC object 59will be created. 60.It 61An integer constant may be specified. 62If 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 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 ORing these constants 79into the 80.Fa flag 81argument: 82.Bl -tag -width 0000 83.It Dv 0400 84Read access for user. 85.It Dv 0200 86Alter access for user. 87.It Dv 0040 88Read access for group. 89.It Dv 0020 90Alter access for group. 91.It Dv 0004 92Read access for other. 93.It Dv 0002 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 104The 105.Fn semget 106system call 107returns the id of a semaphore set if successful; otherwise, -1 108is returned and 109.Va errno 110is set to indicate the error. 111.Sh ERRORS 112The 113.Fn semget 114system call 115will fail if: 116.Bl -tag -width Er 117.\" ipcperm could fail (we are opening to read and write, as it were) 118.It Bq Er EACCES 119Access permission failure. 120.\" 121.\" sysv_sem.c is quite explicit about these, so I'm pretty sure 122.\" this is accurate 123.\" 124.It Bq Er EEXIST 125IPC_CREAT and IPC_EXCL were specified, and a semaphore set 126corresponding to 127.Fa key 128already exists. 129.It Bq Er EINVAL 130The number of semaphores requested exceeds the system imposed maximum 131per set. 132.It Bq Er EINVAL 133A semaphore set corresponding to 134.Fa key 135already exists and contains fewer semaphores than 136.Fa nsems . 137.It Bq Er EINVAL 138A semaphore set corresponding to 139.Fa key 140does not exist and 141.Fa nsems 142is 0 or negative. 143.It Bq Er ENOSPC 144Insufficiently many semaphores are available. 145.It Bq Er ENOSPC 146The kernel could not allocate a 147.Fa "struct semid_ds" . 148.It Bq Er ENOENT 149No semaphore set was found corresponding to 150.Fa key , 151and IPC_CREAT was not specified. 152.El 153.Sh SEE ALSO 154.Xr semctl 2 , 155.Xr semop 2 , 156.Xr ftok 3 157