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System Callssemget(2)


 semget - get set of semaphores


#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/sem.h>
int semget(key_t key, int nsems, int semflg);



The semget() function returns the semaphore identifier associated with key.

A semaphore identifier and associated data structure and set containing nsems semaphores (see intro(2)) are created for key if one of the following is true:

  • key is equal to IPC_PRIVATE.
  • key does not already have a semaphore identifier associated with it, and (semflg&IPC_CREAT) is true.

On creation, the data structure associated with the new semaphore identifier is initialized as follows:

  • sem_perm.cuid, sem_perm.uid, sem_perm.cgid, and sem_perm.gid are set equal to the effective user ID and effective group ID, respectively, of the calling process.
  • The access permission bits of sem_perm.mode are set equal to the access permission bits of semflg.
  • sem_nsems is set equal to the value of nsems.
  • sem_otime is set equal to 0 and sem_ctime is set equal to the current time.



Upon successful completion, a non-negative integer representing a semaphore identifier is returned. Otherwise, -1 is returned and errno is set to indicate the error.



The semget() function will fail if:

A semaphore identifier exists for key, but operation permission (see intro(2)) as specified by the low-order 9 bits of semflg would not be granted.
A semaphore identifier exists for key but both (semflg&IPC_CREAT) and (semflg&IPC_EXCL) are both true.
The nsems argument is either less than or equal to 0 or greater than the system-imposed limit; or a semaphore identifier exists for key, but the number of semaphores in the set associated with it is less than nsems and nsems is not equal to 0.
A semaphore identifier does not exist for key and (semflg&IPC_CREAT) is false.
A semaphore identifier is to be created but the system-imposed limit on the maximum number of allowed semaphores or semaphore identifiers system-wide would be exceeded.



ipcrm(1), ipcs(1), intro(2), semctl(2), semop(2), ftok(3C)

SunOS 5.9Go To TopLast Changed 30 Nov 1993

Copyright 2002 Sun Microsystems, Inc. All rights reserved. Use is subject to license terms.