.\" $OpenBSD: shmget.2,v 1.2 1996/10/08 01:20:16 michaels Exp $ .\" $NetBSD: shmget.2,v 1.1 1995/10/16 23:49:32 jtc Exp $ .\" .\" Copyright (c) 1995 Frank van der Linden .\" All rights reserved. .\" .\" Redistribution and use in source and binary forms, with or without .\" modification, are permitted provided that the following conditions .\" are met: .\" 1. Redistributions of source code must retain the above copyright .\" notice, this list of conditions and the following disclaimer. .\" 2. Redistributions in binary form must reproduce the above copyright .\" notice, this list of conditions and the following disclaimer in the .\" documentation and/or other materials provided with the distribution. .\" 3. All advertising materials mentioning features or use of this software .\" must display the following acknowledgement: .\" This product includes software developed for the NetBSD Project .\" by Frank van der Linden .\" 4. The name of the author may not be used to endorse or promote products .\" derived from this software without specific prior written permission .\" .\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR .\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES .\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. .\" IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, .\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT .\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, .\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY .\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT .\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF .\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. .\"/ .Dd August 17, 1995 .Dt SHMGET 2 .Os .Sh NAME .Nm shmget .Nd get shared memory area identifier .Sh SYNOPSIS .Fd #include <sys/shm.h> .Ft int .Fo shmget .Fa "key_t key" .Fa "size_t size" .Fa "int shmflg" .Fc .Sh DESCRIPTION .Fn shmget returns the shared memory identifier associated with the key .Fa key . .Pp A shared memory segment is created if either .Fa key is equal to IPC_PRIVATE, or .Fa key does not have a shared memory segment identifier associated with it, and the IPC_CREAT bit is set in .Fa shmflg. .Pp If a new shared memory segment is created, the data structure associated with it (the .Va shmid_ds structure, see .Xr shmctl 2 ) is initialized as follows: .Bl -bullet .It .Va shm_perm.cuid and .Va shm_perm.uid are set to the effective uid of the calling process. .It .Va shm_perm.gid and .Va shm_perm.cgid are set to the effective gid of the calling process. .It .Va shm_perm.mode is set to the lower 9 bits of .Fa shmflg . .It .Va shm_lpid , .Va shm_nattch , .Va shm_atime , and .Va shm_dtime are set to 0 .It .Va shm_ctime is set to the current time. .It .Va shm_segsz is set to the value of .Fa size . .It The .Xr ftok 3 function may be used to generate a key from a pathname. .El .Sh RETURN VALUES Upon successful completion a positive shared memory segment identifier is returned. Otherwise, -1 is returned and the global variable .Va errno is set to indicate the error. .Sh ERRORS The .Fn shmget system call will fail if: .Bl -tag -width Er .\" =========== .It Bq Er EACCES A shared memory segment is already associated with .Fa key and the caller has no permission to access it. .\" =========== .It Bq Er EEXIST Both IPC_CREAT and IPC_EXCL are set in .Fa shmflg , and a shared memory segment is already associated with .Fa key . .\" =========== .It Bq Er EINVAL No shared memory segment is to be created, and a shared memory segment exists for .Fa key , but the size of the segment associated with it is less than .Fa size , which is non-zero. .\" =========== .It Bq Er ENOENT IPC_CREAT was not set in .Fa shmflg and no shared memory segment associated with .Fa key was found. .\" =========== .It Bq Er ENOMEM There is not enough memory left to created a shared memory segment of the requested size. .\" =========== .It Bq Er ENOSPC A new shared memory identifier could not be created because the system limit for the number of shared memory identifiers has been reached. .El .Sh LEGACY SYNOPSIS .Fd #include <sys/types.h> .Fd #include <sys/ipc.h> .Fd #include <sys/shm.h> .Pp .Ft int .br .Fo shmget .Fa "key_t key" .Fa "int size" .Fa "int shmflg" .Fc ; .Pp All of these include files are necessary. The type of .Fa size has changed. .Sh SEE ALSO .Xr ftok 3 , .Xr shmat 2 , .Xr shmctl 2 , .Xr shmdt 2 , .Xr compat 5