1.\" $OpenBSD: shmget.2,v 1.17 2014/11/15 22:19:53 guenther Exp $ 2.\" $NetBSD: shmget.2,v 1.2 1997/03/27 08:20:39 mikel Exp $ 3.\" 4.\" Copyright (c) 1995 Frank van der Linden 5.\" All rights reserved. 6.\" 7.\" Redistribution and use in source and binary forms, with or without 8.\" modification, are permitted provided that the following conditions 9.\" are met: 10.\" 1. Redistributions of source code must retain the above copyright 11.\" notice, this list of conditions and the following disclaimer. 12.\" 2. Redistributions in binary form must reproduce the above copyright 13.\" notice, this list of conditions and the following disclaimer in the 14.\" documentation and/or other materials provided with the distribution. 15.\" 3. All advertising materials mentioning features or use of this software 16.\" must display the following acknowledgement: 17.\" This product includes software developed for the NetBSD Project 18.\" by Frank van der Linden 19.\" 4. The name of the author may not be used to endorse or promote products 20.\" derived from this software without specific prior written permission 21.\" 22.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR 23.\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES 24.\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. 25.\" IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, 26.\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT 27.\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, 28.\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY 29.\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT 30.\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF 31.\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 32.\"/ 33.Dd $Mdocdate: November 15 2014 $ 34.Dt SHMGET 2 35.Os 36.Sh NAME 37.Nm shmget 38.Nd get shared memory area identifier 39.Sh SYNOPSIS 40.In sys/shm.h 41.Ft int 42.Fn shmget "key_t key" "size_t size" "int shmflg" 43.Sh DESCRIPTION 44.Fn shmget 45returns the shared memory identifier associated with the key 46.Fa key . 47.Pp 48A shared memory segment is created if either 49.Fa key 50is equal to 51.Dv IPC_PRIVATE , 52or 53.Fa key 54does not have a shared memory segment identifier associated with it, and the 55.Dv IPC_CREAT 56bit is set in 57.Fa shmflg . 58.Pp 59If a new shared memory segment is created, the data structure associated with 60it (the 61.Va shmid_ds 62structure, see 63.Xr shmctl 2 ) 64is initialized as follows: 65.Bl -bullet 66.It 67.Va shm_perm.cuid 68and 69.Va shm_perm.uid 70are set to the effective uid of the calling process. 71.It 72.Va shm_perm.gid 73and 74.Va shm_perm.cgid 75are set to the effective gid of the calling process. 76.It 77.Va shm_perm.mode 78is set to the lower 9 bits of 79.Fa shmflg . 80.It 81.Va shm_lpid , 82.Va shm_nattch , 83.Va shm_atime , 84and 85.Va shm_dtime 86are set to 0. 87.It 88.Va shm_ctime 89is set to the current time. 90.It 91.Va shm_segsz 92is set to the value of 93.Fa size . 94.El 95.Sh RETURN VALUES 96Upon successful completion a positive shared memory segment identifier is 97returned. 98Otherwise, \-1 is returned and the global variable 99.Va errno 100is set to indicate the error. 101.Sh ERRORS 102.Bl -tag -width Er 103.It Bq Er EACCES 104A shared memory segment is already associated with 105.Fa key 106and the caller has no permission to access it. 107.It Bq Er EEXIST 108Both 109.Dv IPC_CREAT 110and 111.Dv IPC_EXCL 112are set in 113.Fa shmflg , 114and a shared memory segment is already associated with 115.Fa key . 116.It Bq Er EINVAL 117A shared memory segment is already associated with 118.Fa key 119and its 120.Fa size 121is less than the requested size. 122.It Bq Er ENOSPC 123A new shared memory identifier could not be created because the system limit 124for the number of shared memory identifiers has been reached. 125.It Bq Er ENOENT 126.Dv IPC_CREAT 127was not set in 128.Fa shmflg 129and no shared memory segment associated with 130.Fa key 131was found. 132.It Bq Er ENOMEM 133There is not enough memory left to create a shared memory segment of the 134requested size. 135.El 136.Sh SEE ALSO 137.Xr ipcrm 1 , 138.Xr ipcs 1 , 139.Xr mmap 2 , 140.Xr shmat 2 , 141.Xr shmctl 2 , 142.Xr ftok 3 143