+++ /dev/null
-.\" Copyright 1993 Giorgio Ciucci (giorgio@crcc.it)
-.\"
-.\" %%%LICENSE_START(VERBATIM)
-.\" Permission is granted to make and distribute verbatim copies of this
-.\" manual provided the copyright notice and this permission notice are
-.\" preserved on all copies.
-.\"
-.\" Permission is granted to copy and distribute modified versions of this
-.\" manual under the conditions for verbatim copying, provided that the
-.\" entire resulting derived work is distributed under the terms of a
-.\" permission notice identical to this one.
-.\"
-.\" Since the Linux kernel and libraries are constantly changing, this
-.\" manual page may be incorrect or out-of-date. The author(s) assume no
-.\" responsibility for errors or omissions, or for damages resulting from
-.\" the use of the information contained herein. The author(s) may not
-.\" have taken the same level of care in the production of this manual,
-.\" which is licensed free of charge, as they might when working
-.\" professionally.
-.\"
-.\" Formatted or processed versions of this manual, if unaccompanied by
-.\" the source, must acknowledge the copyright and authors of this work.
-.\" %%%LICENSE_END
-.\"
-.\" Modified Tue Oct 22 17:54:56 1996 by Eric S. Raymond <esr@thyrsus.com>
-.\" Modified 1 Jan 2002, Martin Schulze <joey@infodrom.org>
-.\" Modified 4 Jan 2002, Michael Kerrisk <mtk.manpages@gmail.com>
-.\" Modified, 27 May 2004, Michael Kerrisk <mtk.manpages@gmail.com>
-.\" Added notes on capability requirements
-.\" Modified, 11 Nov 2004, Michael Kerrisk <mtk.manpages@gmail.com>
-.\" Language and formatting clean-ups
-.\" Added notes on /proc files
-.\" Rewrote BUGS note about semget()'s failure to initialize
-.\" semaphore values
-.\"
-.TH SEMGET 2 2014-05-21 "Linux" "Linux Programmer's Manual"
-.SH NAME
-semget \- get a System V semaphore set identifier
-.SH SYNOPSIS
-.nf
-.B #include <sys/types.h>
-.B #include <sys/ipc.h>
-.B #include <sys/sem.h>
-.fi
-.sp
-.BI "int semget(key_t " key ,
-.BI "int " nsems ,
-.BI "int " semflg );
-.SH DESCRIPTION
-The
-.BR semget ()
-system call returns the System\ V semaphore set identifier
-associated with the argument
-.IR key .
-A new set of
-.I nsems
-semaphores is created if
-.I key
-has the value
-.B IPC_PRIVATE
-or if no existing semaphore set is associated with
-.I key
-and
-.B IPC_CREAT
-is specified in
-.IR semflg .
-.PP
-If
-.I semflg
-specifies both
-.B IPC_CREAT
-and
-.B IPC_EXCL
-and a semaphore set already exists for
-.IR key ,
-then
-.BR semget ()
-fails with
-.I errno
-set to
-.BR EEXIST .
-(This is analogous to the effect of the combination
-.B O_CREAT | O_EXCL
-for
-.BR open (2).)
-.PP
-Upon creation, the least significant 9 bits of the argument
-.I semflg
-define the permissions (for owner, group and others)
-for the semaphore set.
-These bits have the same format, and the same
-meaning, as the
-.I mode
-argument of
-.BR open (2)
-(though the execute permissions are
-not meaningful for semaphores, and write permissions mean permission
-to alter semaphore values).
-.PP
-When creating a new semaphore set,
-.BR semget ()
-initializes the set's associated data structure,
-.I semid_ds
-(see
-.BR semctl (2)),
-as follows:
-.IP
-.I sem_perm.cuid
-and
-.I sem_perm.uid
-are set to the effective user ID of the calling process.
-.IP
-.I sem_perm.cgid
-and
-.I sem_perm.gid
-are set to the effective group ID of the calling process.
-.IP
-The least significant 9 bits of
-.I sem_perm.mode
-are set to the least significant 9 bits of
-.IR semflg .
-.IP
-.I sem_nsems
-is set to the value of
-.IR nsems .
-.IP
-.I sem_otime
-is set to 0.
-.IP
-.I sem_ctime
-is set to the current time.
-.PP
-The argument
-.I nsems
-can be 0
-(a don't care)
-when a semaphore set is not being created.
-Otherwise,
-.I nsems
-must be greater than 0
-and less than or equal to the maximum number of semaphores per semaphore set
-.RB ( SEMMSL ).
-.PP
-If the semaphore set already exists, the permissions are
-verified.
-.\" and a check is made to see if it is marked for destruction.
-.SH RETURN VALUE
-If successful, the return value will be the semaphore set identifier
-(a nonnegative integer), otherwise, \-1
-is returned, with
-.I errno
-indicating the error.
-.SH ERRORS
-On failure,
-.I errno
-will be set to one of the following:
-.TP
-.B EACCES
-A semaphore set exists for
-.IR key ,
-but the calling process does not have permission to access the set,
-and does not have the
-.B CAP_IPC_OWNER
-capability.
-.TP
-.B EEXIST
-.B IPC_CREAT
-and
-.BR IPC_EXCL
-were specified in
-.IR semflg ,
-but a semaphore set already exists for
-.IR key .
-.\" .TP
-.\" .B EIDRM
-.\" The semaphore set is marked to be deleted.
-.TP
-.B EINVAL
-.I nsems
-is less than 0 or greater than the limit on the number
-of semaphores per semaphore set
-.RB ( SEMMSL ).
-.TP
-.B EINVAL
-A semaphore set corresponding to
-.I key
-already exists, but
-.I nsems
-is larger than the number of semaphores in that set.
-.TP
-.B ENOENT
-No semaphore set exists for
-.I key
-and
-.I semflg
-did not specify
-.BR IPC_CREAT .
-.TP
-.B ENOMEM
-A semaphore set has to be created but the system does not have
-enough memory for the new data structure.
-.TP
-.B ENOSPC
-A semaphore set has to be created but the system limit for the maximum
-number of semaphore sets
-.RB ( SEMMNI ),
-or the system wide maximum number of semaphores
-.RB ( SEMMNS ),
-would be exceeded.
-.SH CONFORMING TO
-SVr4, POSIX.1-2001.
-.\" SVr4 documents additional error conditions EFBIG, E2BIG, EAGAIN,
-.\" ERANGE, EFAULT.
-.SH NOTES
-The inclusion of
-.I <sys/types.h>
-and
-.I <sys/ipc.h>
-isn't required on Linux or by any version of POSIX.
-However,
-some old implementations required the inclusion of these header files,
-and the SVID also documented their inclusion.
-Applications intended to be portable to such old systems may need
-to include these header files.
-.\" Like Linux, the FreeBSD man pages still document
-.\" the inclusion of these header files.
-
-.B IPC_PRIVATE
-isn't a flag field but a
-.I key_t
-type.
-If this special value is used for
-.IR key ,
-the system call ignores all but the least significant 9 bits of
-.I semflg
-and creates a new semaphore set (on success).
-.\"
-.SS Semaphore initialization
-The values of the semaphores in a newly created set are indeterminate.
-(POSIX.1-2001 and POSIX.1-2008 are explicit on this point,
-although POSIX.1-2008 notes that a future version of the standard
-may require an implementation to initialize the semaphores to 0.)
-Although Linux, like many other implementations,
-initializes the semaphore values to 0,
-a portable application cannot rely on this:
-it should explicitly initialize the semaphores to the desired values.
-.\" In truth, every one of the many implementations that I've tested sets
-.\" the values to zero, but I suppose there is/was some obscure
-.\" implementation out there that does not.
-
-Initialization can be done using
-.BR semctl (2)
-.B SETVAL
-or
-.B SETALL
-operation.
-Where multiple peers do not know who will be the first to
-initialize the set, checking for a nonzero
-.I sem_otime
-in the associated data structure retrieved by a
-.BR semctl (2)
-.B IPC_STAT
-operation can be used to avoid races.
-.\"
-.SS Semaphore limits
-The following limits on semaphore set resources affect the
-.BR semget ()
-call:
-.TP
-.B SEMMNI
-System-wide limit on the number of semaphore sets: policy dependent
-(on Linux, this limit can be read and modified via the fourth field of
-.IR /proc/sys/kernel/sem ).
-.\" This /proc file is not available in Linux 2.2 and earlier -- MTK
-.TP
-.B SEMMSL
-Maximum number of semaphores per semaphore ID: implementation dependent
-(on Linux, this limit can be read and modified via the first field of
-.IR /proc/sys/kernel/sem ).
-.TP
-.B SEMMNS
-System-wide limit on the number of semaphores: policy dependent
-(on Linux, this limit can be read and modified via the second field of
-.IR /proc/sys/kernel/sem ).
-Note that the number of semaphores system-wide
-is also limited by the product of
-.B SEMMSL
-and
-.BR SEMMNI .
-.SH BUGS
-The name choice
-.B IPC_PRIVATE
-was perhaps unfortunate,
-.B IPC_NEW
-would more clearly show its function.
-.SH SEE ALSO
-.BR semctl (2),
-.BR semop (2),
-.BR ftok (3),
-.BR capabilities (7),
-.BR sem_overview (7),
-.BR svipc (7)
-.SH COLOPHON
-This page is part of release 3.79 of the Linux
-.I man-pages
-project.
-A description of the project,
-information about reporting bugs,
-and the latest version of this page,
-can be found at
-\%http://www.kernel.org/doc/man\-pages/.
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