mirror of https://github.com/mkerrisk/man-pages
157 lines
3.7 KiB
Groff
157 lines
3.7 KiB
Groff
'\" t
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.\" Hey Emacs! This file is -*- nroff -*- source.
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.\"
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.\" Copyright (C) 2006 Michael Kerrisk <mtk-manpages@gmx.net>
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.\"
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.\" Permission is granted to make and distribute verbatim copies of this
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.\" manual provided the copyright notice and this permission notice are
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.\" preserved on all copies.
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.\"
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.\" Permission is granted to copy and distribute modified versions of this
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.\" manual under the conditions for verbatim copying, provided that the
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.\" entire resulting derived work is distributed under the terms of a
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.\" permission notice identical to this one.
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.\"
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.\" Since the Linux kernel and libraries are constantly changing, this
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.\" manual page may be incorrect or out-of-date. The author(s) assume no
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.\" responsibility for errors or omissions, or for damages resulting from
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.\" the use of the information contained herein.
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.\"
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.\" Formatted or processed versions of this manual, if unaccompanied by
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.\" the source, must acknowledge the copyright and authors of this work.
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.\"
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.TH SEM_OPEN 3 2006-03-25 "Linux 2.6.16" "Linux Programmer's Manual"
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.SH NAME
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sem_open \- initialise and open a named semaphore
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.SH SYNOPSIS
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.nf
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.B #include <semaphore.h>
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.sp
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.BI "sem_t *sem_open(const char *" name ", int " oflag );
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.BI "sem_t *sem_open(const char *" name ", int " oflag ", "
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.BI " mode_t " mode ", unsigned int " value );
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.fi
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.SH DESCRIPTION
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.BR sem_open ()
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creates a new POSIX semaphore or opens an existing semaphore.
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The semaphore is identified by
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.IR name .
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For details of the construction of
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.IR name ,
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see
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.BR sem_overview (7).
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The
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.I oflag
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argument specifies flags that control the operation of the call.
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If
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.B O_CREAT
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is specified in
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.IR oflag ,
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then the semaphore is created if
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it does not already exist.
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The owner (user ID) of the semaphore is set to the effective
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user ID of the calling process.
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The group ownership (group ID) is set to the effective group ID
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of the calling process.
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.\" In reality the file system IDs are used on Linux.
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If both
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.B O_CREAT
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and
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.B O_EXCL
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are specified in
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.IR oflag ,
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then an error is returned if a semaphore with the given
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.I name
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already exists.
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.PP
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If
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.B O_CREAT
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is specified in
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.IR oflag ,
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then two additional arguments must be supplied.
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The
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.I mode
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argument specifies the permissions to be placed on the new semaphore,
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as for
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.BR open (2).
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The permissions settings are masked against the process umask.
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Both read and write permission should be granted to each class of
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user that will access the semaphore.
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The
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.I value
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argument specifies the initial value for the new semaphore.
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If
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.B O_CREAT
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is specified, and a semaphore with the given
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.I name
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already exists, then
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.I mode
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and
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.I value
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are ignored.
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.SH RETURN VALUE
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On success,
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.BR sem_open ()
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returns a the address of the new semaphore;
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this address is used when calling other semaphore-related functions.
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On error,
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.BR sem_open ()
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returns
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.BR SEM_FAILED ,
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with
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.I errno
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set to indicate the error.
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.SH ERRORS
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.TP
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.B EACCESS
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The semaphore exists, but the caller does not have permission to
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open it.
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.TP
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.B EEXIST
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Both
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.B O_CREAT
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and
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.B O_EXCL
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were specified in
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.IR oflag ,
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but a semaphore with this
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.I name
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already exists.
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.TP
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.B EINVAL
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.I value
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was greater than
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.BR SEM_VALUE_MAX .
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.TP
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.B EMFILE
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The process already has the maximum number of files and open.
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.TP
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.B ENAMETOOLONG
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.IR name
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was too long.
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.TP
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.B ENFILE
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The system limit on the total number of open files has been reached.
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.TP
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.B ENOENT
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The
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.B O_CREAT
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flag was not specified in
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.IR oflag ,
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and no semaphore with this
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.I name
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exists.
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.TP
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.B ENOMEM
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Insufficient memory.
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.SH CONFORMING TO
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POSIX.1-2001.
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.SH "SEE ALSO"
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.BR sem_close (3),
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.BR sem_getvalue (3),
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.BR sem_post (3),
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.BR sem_unlink (3),
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.BR sem_wait (3),
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.BR sem_overview (7)
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