1.\" $OpenBSD: shm_open.3,v 1.5 2015/05/05 06:29:15 guenther Exp $ 2.\" 3.\" Copyright (c) 2013 Ted Unangst <tedu@openbsd.org> 4.\" 5.\" Permission to use, copy, modify, and distribute this software for any 6.\" purpose with or without fee is hereby granted, provided that the above 7.\" copyright notice and this permission notice appear in all copies. 8.\" 9.\" THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES 10.\" WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF 11.\" MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR 12.\" ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES 13.\" WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN 14.\" ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF 15.\" OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE. 16.\" 17.Dd $Mdocdate: May 5 2015 $ 18.Dt SHM_OPEN 3 19.Os 20.Sh NAME 21.Nm shm_open , 22.Nm shm_unlink , 23.Nm shm_mkstemp 24.Nd create and destroy shared memory objects 25.Sh SYNOPSIS 26.In sys/mman.h 27.Ft int 28.Fn shm_open "const char *path" "int flags" "mode_t mode" 29.Ft int 30.Fn shm_unlink "const char *path" 31.Ft int 32.Fn shm_mkstemp "char *template" 33.Sh DESCRIPTION 34The 35.Fn shm_open 36function opens a shared memory object and returns a file descriptor suitable 37for use with 38.Xr mmap 2 . 39The 40.Fa flags 41argument has the same meaning as provided to 42.Xr open 2 43and must include at least 44.Dv O_RDONLY 45or 46.Dv O_RDWR 47and may also include a combination of 48.Dv O_CREAT , O_EXCL , O_CLOEXEC , O_NOFOLLOW , 49or 50.Dv O_TRUNC . 51This implementation forces the 52.Fa mode 53to be 0600 or 0400, and prohibits sharing between different UIDs. 54.Pp 55.Fn shm_unlink 56is used to remove a shared memory object. 57The object is not freed until all references to it have been released via 58.Xr close 2 . 59.Pp 60If a temporary shared memory object is desired, the 61.Fn shm_mkstemp 62function should be preferred as it avoids several possible security 63holes that tend to appear in programs trying to create their own unique 64temporary names. 65The 66.Fa template 67argument is a string with at least six trailing Xs as described in 68.Xr mkstemp 3 . 69.Sh RETURN VALUES 70.Fn shm_open 71and 72.Fn shm_mkstemp 73return a file descriptor on successful completion. 74They may fail for any of the reasons listed in 75.Xr open 2 . 76.Sh SEE ALSO 77.Xr mmap 2 78.Sh STANDARDS 79.Fn shm_open 80and 81.Fn shm_unlink 82appear in 83.St -p1003.1-2001 . 84Using 85.Dv O_CLOEXEC 86or 87.Dv O_NOFOLLOW 88with 89.Fn shm_open 90is an extension to that standard. 91This implementation deviates from the standard by permitting less sharing. 92.Pp 93.Fn shm_mkstemp 94is an extension. 95.Sh HISTORY 96The 97.Fn shm_open , 98.Fn shm_unlink , 99and 100.Fn shm_mkstemp 101functions have been available since 102.Ox 5.4 . 103.Sh AUTHORS 104.An Ted Unangst Aq Mt tedu@openbsd.org . 105