.\" .\" Copyright (c) 1995 David Hovemeyer .\" .\" 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. .\" .\" THIS SOFTWARE IS PROVIDED BY THE DEVELOPERS ``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 DEVELOPERS 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. .\" .\" $FreeBSD: src/lib/libc/sys/semctl.2,v 1.9.2.6 2002/03/11 08:37:47 maxim Exp $ .\" .Dd January 4, 2014 .Dt SEMCTL 2 .Os .Sh NAME .Nm semctl .Nd control operations on a semaphore set .Sh LIBRARY .Lb libc .Sh SYNOPSIS .In sys/types.h .In sys/ipc.h .In sys/sem.h .Ft int .Fn semctl "int semid" "int semnum" "int cmd" ... .Sh DESCRIPTION .Fn Semctl performs the operation indicated by .Fa cmd on the semaphore set indicated by .Fa semid . A fourth argument, a .Fa "union semun arg" , is required for certain values of .Fa cmd . For the commands that use the .Fa arg parameter, .Fa "union semun" is defined as follows: .Bd -literal .\" .\" From : .\" union semun { int val; /* value for SETVAL */ struct semid_ds *buf; /* buffer for IPC_STAT & IPC_SET */ u_short *array; /* array for GETALL & SETALL */ }; .Ed .Pp Commands are performed as follows: .\" .\" This section based on Stevens, _Advanced Programming in the UNIX .\" Environment_. .\" .Bl -tag -width ".Dv IPC_RMID" .It Dv IPC_STAT Fetch the semaphore set's .Fa "struct semid_ds" , storing it in the memory pointed to by .Fa arg.buf . .It Dv IPC_SET Changes the .Fa sem_perm.uid , .Fa sem_perm.gid , and .Fa sem_perm.mode members of the semaphore set's .Fa "struct semid_ds" to match those of the struct pointed to by .Fa arg.buf . The calling process's effective uid must match either .Fa sem_perm.uid or .Fa sem_perm.cuid , or it must have superuser privileges. .It Dv IPC_RMID Immediately removes the semaphore set from the system. The calling process's effective uid must equal the semaphore set's .Fa sem_perm.uid or .Fa sem_perm.cuid , or the process must have superuser privileges. .It Dv GETVAL Return the value of semaphore number .Fa semnum . .It Dv SETVAL Set the value of semaphore number .Fa semnum to .Fa arg.val . .It Dv GETPID Return the pid of the last process to perform an operation on semaphore number .Fa semnum . .It Dv GETNCNT Return the number of processes waiting for semaphore number .Fa semnum Ns 's value to become greater than its current value. .It Dv GETZCNT Return the number of processes waiting for semaphore number .Fa semnum Ns 's value to become 0. .It Dv GETALL Fetch the value of all of the semaphores in the set into the array pointed to by .Fa arg.array . .It Dv SETALL Set the values of all of the semaphores in the set to the values in the array pointed to by .Fa arg.array . .El .Pp The .Fa "struct semid_ds" is defined as follows: .Bd -literal .\" .\" Taken straight from . .\" struct semid_ds { struct ipc_perm sem_perm; /* operation permission struct */ struct sem *sem_base; /* pointer to first semaphore in set */ u_short sem_nsems; /* number of sems in set */ time_t sem_otime; /* last operation time */ long sem_pad1; /* SVABI/386 says I need this here */ time_t sem_ctime; /* last change time */ /* Times measured in secs since */ /* 00:00:00 GMT, Jan. 1, 1970 */ long sem_pad2; /* SVABI/386 says I need this here */ long sem_pad3[4]; /* SVABI/386 says I need this here */ }; .Ed .Sh RETURN VALUES On success, when .Fa cmd is one of .Dv GETVAL , GETPID , GETNCNT or .Dv GETZCNT , .Fn semctl returns the corresponding value; otherwise, 0 is returned. On failure, -1 is returned, and .Va errno is set to indicate the error. .Sh ENVIRONMENT The XSI Interprocess Communication family of functions is also available as an implementation in userspace. To use it, the .Xr sysvipcd 8 daemon has to be running. .Pp If the .Ev USR_SYSVIPC variable is set in a process' environment, the process and its children will use the userspace implementation. .Sh ERRORS .Fn Semctl will fail if: .Bl -tag -width Er .It Bq Er EINVAL No semaphore set corresponds to .Fa semid . .It Bq Er EINVAL .Fa semnum is not in the range of valid semaphores for given semaphore set. .It Bq Er EPERM The calling process's effective uid does not match the uid of the semaphore set's owner or creator. .It Bq Er EACCES Permission denied due to mismatch between operation and mode of semaphore set. .El .Sh SEE ALSO .Xr semget 2 , .Xr semop 2 .Sh AUTHORS .An -nosplit The .Dx specific userspace implementation (see .Sx ENVIRONMENT ) was written by .An Larisa Grigore .