2fe8fb192f
There is important information about booting non-ack images in docs/UPDATING. ack/aout-format images can't be built any more, and booting clang/ELF-format ones is a little different. Updating to the new boot monitor is recommended. Changes in this commit: . drop boot monitor -> allowing dropping ack support . facility to copy ELF boot files to /boot so that old boot monitor can still boot fairly easily, see UPDATING . no more ack-format libraries -> single-case libraries . some cleanup of OBJECT_FMT, COMPILER_TYPE, etc cases . drop several ack toolchain commands, but not all support commands (e.g. aal is gone but acksize is not yet). . a few libc files moved to netbsd libc dir . new /bin/date as minix date used code in libc/ . test compile fix . harmonize includes . /usr/lib is no longer special: without ack, /usr/lib plays no kind of special bootstrapping role any more and bootstrapping is done exclusively through packages, so releases depend even less on the state of the machine making them now. . rename nbsd_lib* to lib* . reduce mtree
244 lines
6.4 KiB
Groff
244 lines
6.4 KiB
Groff
.\" $NetBSD: semctl.2,v 1.20 2010/03/22 19:30:55 joerg Exp $
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.\"
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.\" Copyright (c) 1995 Frank van der Linden
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.\" All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\" 3. All advertising materials mentioning features or use of this software
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.\" must display the following acknowledgement:
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.\" This product includes software developed for the NetBSD Project
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.\" by Frank van der Linden
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.\" 4. The name of the author may not be used to endorse or promote products
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.\" derived from this software without specific prior written permission
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
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.\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
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.\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
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.\" IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
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.\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
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.\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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.\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
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.\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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.\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
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.\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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.\"
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.Dd August 25, 1999
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.Dt SEMCTL 2
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.Os
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.Sh NAME
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.Nm semctl
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.Nd semaphore control operations
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.Sh LIBRARY
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.Lb libc
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.Sh SYNOPSIS
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.In sys/sem.h
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.Ft int
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.Fn semctl "int semid" "int semnum" "int cmd" "..."
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.Sh DESCRIPTION
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The
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.Fn semctl
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system call provides a number of control operations on the semaphore specified
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by
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.Fa semnum
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and
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.Fa semid .
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The operation to be performed is specified in
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.Fa cmd
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(see below).
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The fourth argument is optional and depends upon the operation requested.
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If required, it is a union of the following fields:
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.Bd -literal
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int val; /* value for SETVAL */
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struct semid_ds *buf; /* buffer for IPC_{STAT,SET} */
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u_short *array; /* array for GETALL \*[Am] SETALL */
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.Ed
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.Pp
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The
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.Sy semid_ds
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structure used in the
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.Dv IPC_SET
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and
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.Dv IPC_STAT
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commands is defined in
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.In sys/sem.h
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and contains the following members:
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.Bd -literal
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struct ipc_perm sem_perm; /* operation permissions */
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unsigned short sem_nsems; /* number of sems in set */
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time_t sem_otime; /* last operation time */
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time_t sem_ctime; /* last change time */
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.Ed
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.Pp
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The
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.Sy ipc_perm
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structure used inside the
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.Sy semid_ds
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structure is defined in
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.In sys/ipc.h
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and contains the following members:
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.Bd -literal
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uid_t cuid; /* creator user id */
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gid_t cgid; /* creator group id */
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uid_t uid; /* user id */
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gid_t gid; /* group id */
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mode_t mode; /* permission (lower 9 bits) */
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.Ed
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.Pp
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.Fn semctl
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provides the following operations:
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.Bl -tag -width IPC_RMIDX
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.It Dv GETVAL
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Return the value of the semaphore.
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.It Dv SETVAL
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Set the value of the semaphore to
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.Fa arg.val ,
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where
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.Fa arg
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is the fourth argument to
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.Fn semctl .
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.It Dv GETPID
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Return the pid of the last process that did an operation on this semaphore.
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.It Dv GETNCNT
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Return the number of processes waiting to acquire the semaphore.
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.It Dv GETZCNT
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Return the number of processes waiting for the value of the semaphore to
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reach 0.
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.It Dv GETALL
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Return the values of all the semaphores associated with
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.Fa semid .
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.It Dv SETALL
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Set the values of all the semaphores that are associated with the semaphore
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identifier
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.Fa semid
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to the corresponding values in
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.Fa arg.array ,
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where
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.Fa arg
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is the fourth argument to
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.Fn semctl .
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.It Dv IPC_STAT
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Gather information about a semaphore and place the information in the
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structure pointed to by
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.Fa arg.buf ,
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where
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.Fa arg
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is the fourth argument to
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.Fn semctl .
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.It Dv IPC_SET
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Set the value of the
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.Va sem_perm.uid ,
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.Va sem_perm.gid
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and
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.Va sem_perm.mode
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fields in the structure associated with the semaphore.
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The values are taken from the corresponding fields in the structure
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pointed to by
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.Fa arg.buf ,
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there
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.Fa arg
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is the fourth argument to
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.Fn semctl .
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This operation can only be executed by the super-user, or a process that
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has an effective user id equal to either
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.Va sem_perm.cuid
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or
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.Va sem_perm.uid
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in the data structure associated with the semaphore.
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.It Dv IPC_RMID
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Remove the semaphores associated with
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.Fa semid
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from the system and destroy the data structures associated with it.
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Only the super-user or a process with an effective uid equal to the
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.Va sem_perm.cuid
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or
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.Va sem_perm.uid
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values in the data structure associated with the semaphore can do this.
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.El
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.Pp
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The permission to read or change a semaphore (see
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.Xr semop 2 )
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is determined by the
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.Va sem_perm.mode
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field in the same way as is
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done with files (see
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.Xr chmod 2 ) ,
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but the effective uid can match either the
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.Va sem_perm.cuid
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field or the
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.Va sem_perm.uid
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field, and the
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effective gid can match either
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.Va sem_perm.cgid
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or
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.Va sem_perm.gid .
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.Sh RETURN VALUES
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For the
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.Dv GETVAL ,
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.Dv GETPID ,
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.Dv GETNCNT ,
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and
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.Dv GETZCNT
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operations,
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.Fn semctl
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returns one of the values described above if successful.
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All other operations will make
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.Fn semctl
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return 0 if no errors occur.
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Otherwise \-1 is returned and
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.Va errno
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set to reflect the error.
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.Sh ERRORS
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.Fn semctl
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will fail if:
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.Bl -tag -width Er
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.It Bq Er EACCES
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The caller has no operation permission for this semaphore.
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.It Bq Er EFAULT
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.Fa arg.buf
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or
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.Fa arg.array
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specifies an invalid address.
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.It Bq Er EINVAL
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.Fa semid
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is not a valid message semaphore identifier.
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.Pp
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.Va cmd
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is not a valid command.
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.It Bq Er EPERM
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.Fa cmd
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is equal to
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.Dv IPC_SET
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or
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.Dv IPC_RMID
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and the caller is not the super-user, nor does
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the effective uid match either the
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.Va sem_perm.uid
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or
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.Va sem_perm.cuid
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fields of the data structure associated with the semaphore.
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.It Bq Er ERANGE
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.Fa cmd
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is equal to
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.Dv SETVAL
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or
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.Dv SETALL
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and the value to be set is greater than the system semaphore maximum value.
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.El
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.Sh SEE ALSO
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.Xr semget 2 ,
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.Xr semop 2
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.Sh STANDARDS
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The
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.Nm
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system call conforms to
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.St -xsh5 .
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.Sh HISTORY
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Semaphores appeared in the first release of
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.At V .
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