SEMGET(2) BSD System Calls Manual SEMGET(2)
semget -- get semaphore set
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.
The access modes of the created semaphores is specified in semflg as a
bitwise OR of zero or more of the following values:
SEM_A alter permission for owner
SEM_R read permission for owner
SEM_A >> 3 alter permission for group
SEM_R >> 3 read permission for group
SEM_A >> 6 alter permission for other
SEM_R >> 6 read permission for other
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
o sem_perm.gid and sem_perm.cgid are set to the effective GID of the
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. 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 or equal to 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 was not set in semflg and no semaphore set
associated with key was found.
semctl(2), semop(2), ftok(3)
BSD April 28, 2017 BSD