1.\" 2.\" Copyright (c) 1995 David Hovemeyer <[email protected]> 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.\" $FreeBSD$ 27.\" 28.Dd October 10, 2015 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 sys/types.h 38.In sys/ipc.h 39.In sys/shm.h 40.Ft int 41.Fn shmctl "int shmid" "int cmd" "struct shmid_ds *buf" 42.Sh DESCRIPTION 43Performs the action specified by 44.Fa cmd 45on the shared memory segment identified by 46.Fa shmid : 47.Bl -tag -width SHM_UNLOCKX 48.It Dv IPC_STAT 49Fetch the segment's 50.Fa "struct shmid_ds" , 51storing it in the memory pointed to by 52.Fa buf . 53.\" 54.\" XXX need to make sure that this is correct for FreeBSD 55.\" 56.It Dv IPC_SET 57Changes the 58.Fa shm_perm.uid , 59.Fa shm_perm.gid , 60and 61.Fa shm_perm.mode 62members of the segment's 63.Fa "struct shmid_ds" 64to match those of the struct pointed to by 65.Fa buf . 66The calling process's effective uid must 67match either 68.Fa shm_perm.uid 69or 70.Fa shm_perm.cuid , 71or it must have superuser privileges. 72.It Dv IPC_RMID 73Removes the segment from the system. 74The removal will not take 75effect until all processes having attached the segment have exited. 76For the operation 77to succeed, the calling process's effective uid must match 78.Fa shm_perm.uid 79or 80.Fa shm_perm.cuid , 81or the process must have superuser privileges. 82If the 83.Va kern.ipc.shm_allow_removed 84.Xr sysctl 3 85variable is set to 0, once the IPC_RMID operation has taken place, 86no further processes will be allowed to attach the segment. 87.\" .It Dv SHM_LOCK 88.\" Locks the segment in memory. The calling process must have 89.\" superuser privileges. Not implemented in FreeBSD. 90.\" .It Dv SHM_UNLOCK 91.\" Unlocks the segment from memory. The calling process must 92.\" have superuser privileges. Not implemented in FreeBSD. 93.El 94.Pp 95The 96.Vt shmid_ds 97structure is defined as follows: 98.\" 99.\" I fiddled with the spaces a bit to make it fit well when viewed 100.\" with nroff, but otherwise it is straight from sys/shm.h 101.\" 102.Bd -literal 103struct shmid_ds { 104 struct ipc_perm shm_perm; /* operation permission structure */ 105 size_t shm_segsz; /* size of segment in bytes */ 106 pid_t shm_lpid; /* process ID of last shared memory op */ 107 pid_t shm_cpid; /* process ID of creator */ 108 int shm_nattch; /* number of current attaches */ 109 time_t shm_atime; /* time of last shmat() */ 110 time_t shm_dtime; /* time of last shmdt() */ 111 time_t shm_ctime; /* time of last change by shmctl() */ 112}; 113.Ed 114.Sh RETURN VALUES 115.Rv -std shmctl 116.Sh ERRORS 117The 118.Fn shmctl 119system call 120will fail if: 121.Bl -tag -width Er 122.It Bq Er EINVAL 123Invalid operation, or 124no shared memory segment was found corresponding to 125.Fa shmid . 126.\" 127.\" XXX I think the following is right: ipcperm() only returns EPERM 128.\" when an attempt is made to modify (IPC_M) by a non-creator 129.\" non-owner 130.It Bq Er EPERM 131The calling process's effective uid does not match the uid of 132the shared memory segment's owner or creator. 133.It Bq Er EACCES 134Permission denied due to mismatch between operation and mode of 135shared memory segment. 136.El 137.Sh "SEE ALSO" 138.Xr shmat 2 , 139.Xr shmdt 2 , 140.Xr shmget 2 , 141.Xr ftok 3 142