1.\" 2.\" Copyright (c) 1995 David Hovemeyer <daveho@infocom.com> 3.\" 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.\" 15.\" THIS SOFTWARE IS PROVIDED BY THE DEVELOPERS ``AS IS'' AND ANY EXPRESS OR 16.\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES 17.\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. 18.\" IN NO EVENT SHALL THE DEVELOPERS BE LIABLE FOR ANY DIRECT, INDIRECT, 19.\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT 20.\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, 21.\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY 22.\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT 23.\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF 24.\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 25.\" 26.\" $FreeBSD: src/lib/libc/sys/shmctl.2,v 1.9.2.4 2001/12/14 18:34:01 ru Exp $ 27.\" 28.Dd January 4, 2014 29.Dt SHMCTL 2 30.Os 31.Sh NAME 32.Nm shmctl 33.Nd shared memory control 34.Sh LIBRARY 35.Lb libc 36.Sh SYNOPSIS 37.In machine/param.h 38.In sys/types.h 39.In sys/ipc.h 40.In sys/shm.h 41.Ft int 42.Fn shmctl "int shmid" "int cmd" "struct shmid_ds *buf" 43.Sh DESCRIPTION 44Performs the action specified by 45.Fa cmd 46on the shared memory segment identified by 47.Fa shmid : 48.Bl -tag -width SHM_UNLOCKX 49.It Dv IPC_STAT 50Fetch the segment's 51.Fa "struct shmid_ds" , 52storing it in the memory pointed to by 53.Fa buf . 54.\" 55.\" XXX need to make sure that this is correct for FreeBSD 56.\" 57.It Dv IPC_SET 58Changes the 59.Fa shm_perm.uid , 60.Fa shm_perm.gid , 61and 62.Fa shm_perm.mode 63members of the segment's 64.Fa "struct shmid_ds" 65to match those of the struct pointed to by 66.Fa buf . 67The calling process's effective uid must 68match either 69.Fa shm_perm.uid 70or 71.Fa shm_perm.cuid , 72or it must have superuser privileges. 73.It Dv IPC_RMID 74Removes the segment from the system. The removal will not take 75effect until all processes having attached the segment have exited; 76however, once the IPC_RMID operation has taken place, no further 77processes will be allowed to attach the segment. For the operation 78to succeed, the calling process's effective uid must match 79.Fa shm_perm.uid 80or 81.Fa shm_perm.cuid , 82or the process must have superuser privileges. 83.\" .It Dv SHM_LOCK 84.\" Locks the segment in memory. The calling process must have 85.\" superuser privileges. Not implemented in FreeBSD. 86.\" .It Dv SHM_UNLOCK 87.\" Unlocks the segment from memory. The calling process must 88.\" have superuser privileges. Not implemented in FreeBSD. 89.El 90.Pp 91The 92.Fa shmid_ds 93struct is defined as follows: 94.\" 95.\" I fiddled with the spaces a bit to make it fit well when viewed 96.\" with nroff, but otherwise it's straight from sys/shm.h 97.\" 98.Bd -literal 99typedef unsigned int shmatt_t; 100 101struct shmid_ds { 102 struct ipc_perm shm_perm; /* operation permission structure */ 103 size_t shm_segsz; /* size of segment in bytes */ 104 pid_t shm_lpid; /* process ID of last shared memory op */ 105 pid_t shm_cpid; /* process ID of creator */ 106 shmatt_t shm_nattch; /* number of current attaches */ 107 time_t shm_atime; /* time of last shmat() */ 108 time_t shm_dtime; /* time of last shmdt() */ 109 time_t shm_ctime; /* time of last change by shmctl() */ 110 void *shm_internal; /* sysv stupidity */ 111}; 112.Ed 113.Sh RETURN VALUES 114.Rv -std shmctl 115.Sh ENVIRONMENT 116The XSI Interprocess Communication family of functions is also available 117as an implementation in userspace. 118To use it, the 119.Xr sysvipcd 8 120daemon has to be running. 121.Pp 122If the 123.Ev USR_SYSVIPC 124variable is set in a process' environment, the process and its children 125will use the userspace implementation. 126.Sh ERRORS 127.Fn Shmctl 128will fail if: 129.Bl -tag -width Er 130.It Bq Er EINVAL 131Invalid operation, or 132no shared memory segment was found corresponding to 133.Fa shmid . 134.\" 135.\" XXX I think the following is right: ipcperm() only returns EPERM 136.\" when an attempt is made to modify (IPC_M) by a non-creator 137.\" non-owner 138.It Bq Er EPERM 139The calling process's effective uid does not match the uid of 140the shared memory segment's owner or creator. 141.It Bq Er EACCES 142Permission denied due to mismatch between operation and mode of 143shared memory segment. 144.El 145.Sh "SEE ALSO" 146.Xr shmat 2 , 147.Xr shmdt 2 , 148.Xr shmget 2 , 149.Xr ftok 3 150.Sh AUTHORS 151.An -nosplit 152The 153.Dx 154specific userspace implementation (see 155.Sx ENVIRONMENT ) 156was written by 157.An Larisa Grigore . 158