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NetBSD 6.1.5 - man page for semget (netbsd section 2)

SEMGET(2)			     BSD System Calls Manual				SEMGET(2)

     semget -- get set of semaphores

     Standard C Library (libc, -lc)

     #include <sys/sem.h>

     semget(key_t key, int nsems, int semflg);

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

     A new set containing nsems semaphores is created if either key is equal to IPC_PRIVATE, or
     key does not have a semaphore set associated with it and the IPC_CREAT bit is set in semflg.
     If both the IPC_CREAT bit and the IPC_EXCL bit are set in semflg, and key has a semaphore
     set associated with it already, the operation will fail.

     If a new set of semaphores is created, the data structure associated with it (the semid_ds
     structure, see semctl(2)) is initialized as follows:

     o	 sem_perm.cuid and sem_perm.uid are set to the effective uid of the calling process.

     o	 sem_perm.gid and sem_perm.cgid are set to the effective gid of the calling process.

     o	 sem_perm.mode is set to the lower 9 bits of semflg.

     o	 sem_nsems is set to the value of nsems.

     o	 sem_ctime is set to the current time.

     o	 sem_otime is set to 0.

     semget() returns a non-negative semaphore identifier if successful.  Otherwise, -1 is
     returned and errno is set to reflect the error.

     [EACCES]		The caller has no permission to access a semaphore set already associated
			with key.

     [EEXIST]		Both IPC_CREAT and IPC_EXCL are set in semflg, and a semaphore set is
			already associated with key.

     [EINVAL]		nsems is less than 0 or greater than the system limit for the number in a
			semaphore set.

			A semaphore set associated with key exists, but has fewer semaphores than
			the number specified in nsems.

     [ENOSPC]		A new set of semaphores could not be created because the system limit for
			the number of semaphores or the number of semaphore sets has been

     [ENOENT]		IPC_CREAT is not set in semflg and no semaphore set associated with key
			was found.

     ipcs(1), semctl(2), semop(2), ftok(3)

     The semget system call conforms to X/Open System Interfaces and Headers Issue 5 (``XSH5'').

     Semaphores appeared in the first release of AT&T System V UNIX.

BSD					   May 13, 2004 				      BSD

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