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semget(3p) — Linux manual page

PROLOG \|NAME \|SYNOPSIS \|DESCRIPTION \|RETURN VALUE \|ERRORS \|EXAMPLES \|APPLICATION USAGE \|RATIONALE \|FUTURE DIRECTIONS \|SEE ALSO \|COPYRIGHT

SEMGET(3P)              POSIX Programmer's ManualSEMGET(3P)

PROLOG top

       This manual page is part of the POSIX Programmer's Manual.  The       Linux implementation of this interface may differ (consult the       corresponding Linux manual page for details of Linux behavior), or       the interface may not be implemented on Linux.

NAME top

       semget — get set of XSI semaphores

SYNOPSIS top

       #include <sys/sem.h>       int semget(key_tkey, intnsems, intsemflg);

DESCRIPTION top

       Thesemget() function operates on XSI semaphores (see the Base       Definitions volume of POSIX.1‐2017,Section 4.17,Semaphore).  It       is unspecified whether this function interoperates with the       realtime interprocess communication facilities defined inSection2.8,Realtime.       Thesemget() function shall return the semaphore identifier       associated withkey.       A semaphore identifier with its associatedsemid_dsdata structure       and its associated set ofnsems semaphores (see<sys/sem.h>) is       created forkey if one of the following is true:        *  The argumentkey is equal to IPC_PRIVATE.        *  The argumentkey does not already have a semaphore identifier           associated with it and (semflg &IPC_CREAT) is non-zero.       Upon creation, thesemid_dsdata structure associated with the new       semaphore identifier is initialized as follows:        *  In the operation permissions structuresem_perm.cuid,sem_perm.uid,sem_perm.cgid, andsem_perm.gid shall be set to           the effective user ID and effective group ID, respectively, of           the calling process.        *  The low-order 9 bits ofsem_perm.mode shall be set to the low-           order 9 bits ofsemflg.        *  The variablesem_nsems shall be set to the value ofnsems.        *  The variablesem_otime shall be set to 0 andsem_ctime shall           be set to the current time, as described inSection 2.7.1,IPCGeneral Description.        *  The data structure associated with each semaphore in the set           need not be initialized. Thesemctl() function with the           command SETVAL or SETALL can be used to initialize each           semaphore.

RETURN VALUE top

       Upon successful completion,semget() shall return a non-negative       integer, namely a semaphore identifier; otherwise, it shall return       -1 and seterrno to indicate the error.

ERRORS top

       Thesemget() function shall fail if:EACCESA semaphore identifier exists forkey, but operation              permission as specified by the low-order 9 bits ofsemflg              would not be granted; seeSection 2.7,XSI InterprocessCommunication.EEXISTA semaphore identifier exists for the argumentkey but              ((semflg &IPC_CREAT) &&(semflg &IPC_EXCL)) is non-zero.EINVALThe value ofnsems is either less than or equal to 0 or              greater than the system-imposed limit, or a semaphore              identifier exists for the argumentkey, but the number of              semaphores in the set associated with it is less thannsems              andnsems is not equal to 0.ENOENTA semaphore identifier does not exist for the argumentkey              and (semflg &IPC_CREAT) is equal to 0.ENOSPCA semaphore identifier is to be created but the system-              imposed limit on the maximum number of allowed semaphores              system-wide would be exceeded.The following sections are informative.

EXAMPLES top

       Refer tosemop(3p).

APPLICATION USAGE top

       The POSIX Realtime Extension defines alternative interfaces for       interprocess communication. Application developers who need to use       IPC should design their applications so that modules using the IPC       routines described inSection 2.7,XSI Interprocess Communication       can be easily modified to use the alternative interfaces.

RATIONALE top

       None.

FUTURE DIRECTIONS top

       A future version may require that the value of thesemval,sempid,semncnt, andsemzcnt members of all semaphores in a semaphore set       be initialized to zero when a call tosemget() creates a semaphore       set. Many semaphore implementations already do this and it greatly       simplifies what an application must do to initialize a semaphore       set.

COPYRIGHT top

       Portions of this text are reprinted and reproduced in electronic       form from IEEE Std 1003.1-2017, Standard for Information       Technology -- Portable Operating System Interface (POSIX), The       Open Group Base Specifications Issue 7, 2018 Edition, Copyright       (C) 2018 by the Institute of Electrical and Electronics Engineers,       Inc and The Open Group.  In the event of any discrepancy between       this version and the original IEEE and The Open Group Standard,       the original IEEE and The Open Group Standard is the referee       document. The original Standard can be obtained online athttp://www.opengroup.org/unix/online.html .       Any typographical or formatting errors that appear in this page       are most likely to have been introduced during the conversion of       the source files to man page format. To report such errors, seehttps://www.kernel.org/doc/man-pages/reporting_bugs.html .IEEE/The Open Group                2017SEMGET(3P)

Pages that refer to this page:sys_sem.h(0p), ipcs(1p), ftok(3p), sem_close(3p), semctl(3p), sem_destroy(3p), sem_getvalue(3p), semop(3p), sem_open(3p), sem_post(3p), sem_timedwait(3p), sem_trywait(3p), sem_unlink(3p), sigaction(3p)