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SEMGET(2) NetBSD System Calls Manual SEMGET(2)
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by Kimmo Suominen.
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semget -- get set of semaphores
Standard C Library (libc, -lc)
semget(key_t key, int nsems, int semflg);
The semget() system call returns the semaphore identifier associated with
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 associ-
ated 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:
· sem_perm.cuid and sem_perm.uid are set to the effective uid of the
· sem_perm.gid and sem_perm.cgid are set to the effective gid of the
· sem_perm.mode is set to the lower 9 bits of semflg.
· sem_nsems is set to the value of nsems.
· sem_ctime is set to the current time.
· sem_otime is set to 0.
semget() returns a non-negative semaphore identifier if successful. Oth-
erwise, -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 reached.
[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.
NetBSD 8.1 May 13, 2004 NetBSD 8.1