1.\" $NetBSD: shmget.2,v 1.22 2008/10/27 16:49:10 wiz Exp $ 2.\" 3.\" Copyright (c) 1995 Frank van der Linden 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.\" 3. All advertising materials mentioning features or use of this software 15.\" must display the following acknowledgement: 16.\" This product includes software developed for the NetBSD Project 17.\" by Frank van der Linden 18.\" 4. The name of the author may not be used to endorse or promote products 19.\" derived from this software without specific prior written permission 20.\" 21.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR 22.\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES 23.\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. 24.\" IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, 25.\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT 26.\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, 27.\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY 28.\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT 29.\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF 30.\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 31.\" 32.Dd October 27, 2008 33.Dt SHMGET 2 34.Os 35.Sh NAME 36.Nm shmget 37.Nd get shared memory segment 38.Sh LIBRARY 39.Lb libc 40.Sh SYNOPSIS 41.In sys/shm.h 42.Ft int 43.Fn shmget "key_t key" "size_t size" "int shmflg" 44.Sh DESCRIPTION 45.Fn shmget 46returns the shared memory identifier associated with the key 47.Fa key . 48.Pp 49A shared memory segment is created if either 50.Fa key 51is equal to 52.Dv IPC_PRIVATE , 53or 54.Fa key 55does not have a shared memory segment identifier associated with it, and the 56.Dv IPC_CREAT 57bit is set in 58.Fa shmflg . 59If both the 60.Dv IPC_CREAT 61bit and the 62.Dv IPC_EXCL 63bit are set in 64.Fa shmflg , 65and 66.Fa key 67has a shared memory segment identifier associated with it already, 68the operation will fail. 69.Pp 70If a new shared memory segment is created, the data structure 71associated with it (the 72.Va shmid_ds 73structure, see 74.Xr shmctl 2 ) 75is initialized as follows: 76.Bl -bullet 77.It 78.Va shm_perm.cuid 79and 80.Va shm_perm.uid 81are set to the effective uid of the calling process. 82.It 83.Va shm_perm.gid 84and 85.Va shm_perm.cgid 86are set to the effective gid of the calling process. 87.It 88.Va shm_perm.mode 89is set to the lower 9 bits of 90.Fa shmflg . 91.It 92.Va shm_lpid , 93.Va shm_nattch , 94.Va shm_atime , 95and 96.Va shm_dtime 97are set to 0. 98.It 99.Va shm_ctime 100is set to the current time. 101.It 102.Va shm_segsz 103is set to the value of 104.Fa size . 105.El 106.Sh RETURN VALUES 107Upon successful completion a positive shared memory segment identifier 108is returned. 109Otherwise, \-1 is returned and the global variable 110.Va errno 111is set to indicate the error. 112.Sh ERRORS 113.Bl -tag -width Er 114.It Bq Er EACCES 115A shared memory segment is already associated with 116.Fa key 117and the caller has no permission to access it. 118.It Bq Er EEXIST 119Both 120.Dv IPC_CREAT 121and 122.Dv IPC_EXCL 123are set in 124.Fa shmflg , 125and a shared memory segment is already associated with 126.Fa key . 127.It Bq Er EINVAL 128No shared memory segment is to be created, and a shared memory segment 129exists for 130.Fa key , 131but the size of the segment associated with it is less 132than 133.Fa size , 134which is non-zero. 135.Pp 136A shared memory segment 137.Em is 138to be created, and 139.Fa size 140is less than the system imposed minimum, or greater than the system 141imposed maximum (refer to the 142.Li kern.ipc 143values in 144.Xr sysctl 7 ) . 145.It Bq Er ENOENT 146.Dv IPC_CREAT 147is not set in 148.Fa shmflg 149and no shared memory segment associated with 150.Fa key 151was found. 152.It Bq Er ENOMEM 153There is not enough memory left to create a shared memory segment of the 154requested size. 155.It Bq Er ENOSPC 156A new shared memory identifier could not be created because the system limit 157for the number of shared memory identifiers has been reached. 158.El 159.Sh SEE ALSO 160.Xr ipcrm 1 , 161.Xr ipcs 1 , 162.Xr mmap 2 , 163.Xr shmat 2 , 164.Xr shmctl 2 , 165.Xr ftok 3 , 166.Xr sysctl 7 167.Sh STANDARDS 168The 169.Nm 170system call conforms to 171.St -xsh5 . 172.Sh HISTORY 173Shared memory segments appeared in the first release of 174.At V . 175