SEMGET(2) BSD System Calls Manual SEMGET(2)
NAME
semget -- get set of semaphores
LIBRARY
Standard C Library (libc, -lc)
SYNOPSIS
#include <sys/sem.h>
int
semget(key_t key, int nsems, int semflg);
DESCRIPTION
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 fol-
lows:
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.
RETURN VALUES
semget() returns a non-negative semaphore identifier if successful. Otherwise, -1 is returned and errno is set to reflect the error.
ERRORS
[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 sema-
phore sets has been reached.
[ENOENT] IPC_CREAT is not set in semflg and no semaphore set associated with key was found.
SEE ALSO
ipcs(1), semctl(2), semop(2), ftok(3)
STANDARDS
The semget system call conforms to X/Open System Interfaces and Headers Issue 5 (``XSH5'').
HISTORY
Semaphores appeared in the first release of AT&T System V UNIX.
BSD
May 13, 2004 BSD
