1.\" $NetBSD: shmget.2,v 1.14 2002/02/08 01:28:22 ross 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 August 25, 1999 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.Fd #include \*[Lt]sys/shm.h\*[Gt] 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 . 48The 49.Fa shmflg 50should be a combination of the following flags: 51.Bl -tag -offset indent -width IPC_NOWAIT 52.It Dv IPC_CREAT 53create if segment does not exist 54.It Dv IPC_EXCL 55fail if segment already exists 56.It Dv IPC_NOWAIT 57return error instead of waiting 58.El 59.Pp 60and nine bits of access bits, based on: 61.Bl -tag -offset indent -width IPC_R 62.It Dv IPC_R 63read permission 64.It Dv IPC_W 65write permission 66.It Dv IPC_M 67changing control info permission 68.El 69.Pp 70A shared memory segment is created if either 71.Fa key 72is equal to 73.Dv IPC_PRIVATE , 74or 75.Fa key 76does not have a shared memory segment identifier associated with it, and the 77.Dv IPC_CREAT 78bit is set in 79.Fa shmflg . 80.Pp 81If a new shared memory segment is created, the data structure 82associated with it (the 83.Va shmid_ds 84structure, see 85.Xr shmctl 2 ) 86is initialized as follows: 87.Bl -bullet 88.It 89.Va shm_perm.cuid 90and 91.Va shm_perm.uid 92are set to the effective uid of the calling process. 93.It 94.Va shm_perm.gid 95and 96.Va shm_perm.cgid 97are set to the effective gid of the calling process. 98.It 99.Va shm_perm.mode 100is set to the lower 9 bits of 101.Fa shmflg . 102.It 103.Va shm_lpid , 104.Va shm_nattch , 105.Va shm_atime , 106and 107.Va shm_dtime 108are set to 0. 109.It 110.Va shm_ctime 111is set to the current time. 112.It 113.Va shm_segsz 114is set to the value of 115.Fa size . 116.El 117.Sh RETURN VALUES 118Upon successful completion a positive shared memory segment identifier 119is returned. 120Otherwise, -1 is returned and the global variable 121.Va errno 122is set to indicate the error. 123.Sh ERRORS 124.Bl -tag -width Er 125.It Bq Er EACCES 126A shared memory segment is already associated with 127.Fa key 128and the caller has no permission to access it. 129.It Bq Er EEXIST 130Both 131.Dv IPC_CREAT 132and 133.Dv IPC_EXCL 134are set in 135.Fa shmflg , 136and a shared memory segment is already associated with 137.Fa key . 138.It Bq Er ENOSPC 139A new shared memory identifier could not be created because the system limit 140for the number of shared memory identifiers has been reached. 141.It Bq Er ENOENT 142.Dv IPC_CREAT 143is not set in 144.Fa shmflg 145and no shared memory segment associated with 146.Fa key 147was found. 148.It Bq Er ENOMEM 149There is not enough memory left to create a shared memory segment of the 150requested size. 151.El 152.Sh SEE ALSO 153.Xr mmap 2 , 154.Xr shmat 2 , 155.Xr shmctl 2 , 156.Xr ftok 3 157.Sh STANDARDS 158The 159.Nm 160system call conforms to 161.St -xsh5 . 162.Sh HISTORY 163Shared memory segments appeared in the first release of 164.At V . 165