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sem_open(3) — Linux manual page

sem_open(3) Library Functions Manual sem_open(3)

NAME top

 sem_open - initialize and open a named semaphore

LIBRARY top

 POSIX threads library (libpthread, -lpthread)

SYNOPSIS top

 #include <fcntl.h> /* For O_* constants */
 #include <sys/stat.h> /* For mode constants */
 #include <semaphore.h>
 sem_t *sem_open(const char *name, int oflag, ...
 /* mode_t mode, unsigned int value */ );

DESCRIPTION top

 sem_open() creates a new POSIX semaphore or opens an existing
 semaphore. The semaphore is identified by name. For details of
 the construction of name, see sem_overview(7).
 The oflag argument specifies flags that control the operation of
 the call. (Definitions of the flags values can be obtained by
 including <fcntl.h>.) If O_CREAT is specified in oflag, then the
 semaphore is created if it does not already exist. The owner
 (user ID) of the semaphore is set to the effective user ID of the
 calling process. The group ownership (group ID) is set to the
 effective group ID of the calling process. If both O_CREAT and
 O_EXCL are specified in oflag, then an error is returned if a
 semaphore with the given name already exists.
 If O_CREAT is specified in oflag, then two additional arguments
 must be supplied. The mode argument specifies the permissions to
 be placed on the new semaphore, as for open(2). (Symbolic
 definitions for the permissions bits can be obtained by including
 <sys/stat.h>.) The permissions settings are masked against the
 process umask. Both read and write permission should be granted
 to each class of user that will access the semaphore. The value
 argument specifies the initial value for the new semaphore. If
 O_CREAT is specified, and a semaphore with the given name already
 exists, then mode and value are ignored.

RETURN VALUE top

 On success, sem_open() returns the address of the new semaphore;
 this address is used when calling other semaphore-related
 functions. On error, sem_open() returns SEM_FAILED, with errno 
 set to indicate the error.

ERRORS top

 EACCES The semaphore exists, but the caller does not have
 permission to open it.
 EEXIST Both O_CREAT and O_EXCL were specified in oflag, but a
 semaphore with this name already exists.
 EINVAL value was greater than SEM_VALUE_MAX.
 EINVAL name consists of just "/", followed by no other characters.
 EMFILE The per-process limit on the number of open file
 descriptors has been reached.
 ENAMETOOLONG
 name was too long.
 ENFILE The system-wide limit on the total number of open files has
 been reached.
 ENOENT The O_CREAT flag was not specified in oflag and no
 semaphore with this name exists; or, O_CREAT was specified,
 but name wasn't well formed.
 ENOMEM Insufficient memory.

ATTRIBUTES top

 For an explanation of the terms used in this section, see
 attributes(7).
 ┌──────────────────────────────────────┬───────────────┬─────────┐
 │ Interface │ Attribute │ Value │
 ├──────────────────────────────────────┼───────────────┼─────────┤
 │ sem_open() │ Thread safety │ MT-Safe │
 └──────────────────────────────────────┴───────────────┴─────────┘

STANDARDS top

 POSIX.1-2008.

HISTORY top

 POSIX.1-2001.

SEE ALSO top

 sem_close(3), sem_getvalue(3), sem_post(3), sem_unlink(3),
 sem_wait(3), sem_overview(7)

COLOPHON top

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 user-space interface documentation) project. Information about
 the project can be found at 
 ⟨https://www.kernel.org/doc/man-pages/⟩. If you have a bug report
 for this manual page, see
 ⟨https://git.kernel.org/pub/scm/docs/man-pages/man-pages.git/tree/CONTRIBUTING⟩.
 This page was obtained from the tarball man-pages-6.10.tar.gz
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 2025年02月02日. If you discover any rendering problems in this HTML
 version of the page, or you believe there is a better or more up-
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 man-pages@man7.org
Linux man-pages 6.10 2025年01月05日 sem_open(3)

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Pages that refer to this page: umask(2), sem_close(3), sem_unlink(3), sem_overview(7)

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