SEMGET(2)SEMGET(2)NAMEsemget - get set of semaphores
SYNOPSIS
#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/sem.h>
int semget(key_t key, int nsems, int semflg);
DESCRIPTION
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 fol‐
lowing is true:
o key is equal to IPC_PRIVATE.
o 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 iden‐
tifier is initialized as follows:
o 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.
o The access permission bits of sem_perm.mode are set equal to
the access permission bits of semflg.
o sem_nsems is set equal to the value of nsems.
o sem_otime is set equal to 0 and sem_ctime is set equal to
the current time.
RETURN VALUES
Upon successful completion, a non-negative integer representing a sema‐
phore identifier is returned. Otherwise, −1 is returned and errno is
set to indicate the error.
ERRORS
The semget() function will fail if:
EACCES
A semaphore identifier exists for key, but operation permis‐
sion (see Intro(2)) as specified by the low-order 9 bits of
semflg would not be granted.
EEXIST
A semaphore identifier exists for key but both (sem‐
flg&IPC_CREAT) and (semflg&IPC_EXCL) are both true.
EINVAL
The nsems argument is either less than or equal to 0 or
greater than the system-imposed limit. See NOTES.
A semaphore identifier exists for key, but the number of sem‐
aphores in the set associated with it is less than nsems and
nsems is not equal to 0.
ENOENT
A semaphore identifier does not exist for key and (sem‐
flg&IPC_CREAT) is false.
ENOSPC
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. See
NOTES.
ATTRIBUTES
See attributes(5) for descriptions of the following attributes:
┌────────────────────┬─────────────────┐
│ ATTRIBUTE TYPE │ ATTRIBUTE VALUE │
├────────────────────┼─────────────────┤
│Interface Stability │ Standard │
└────────────────────┴─────────────────┘
SEE ALSOipcrm(1), ipcs(1), rctladm(1M), Intro(2), semctl(2), semop(2),
setrctl(2), ftok(3C), attributes(5), standards(5)NOTES
The system-imposed limit on the value of the nsems argument is the
maintained on a per-process basis using the process.max-sem-nsems
resource control.
The system-imposed limit on the number of semaphore identifiers is
maintained on a per-project basis using the project.max-sem-ids
resource control. The zone.max-sem-ids resource control limis the
total number of semaphore identifiers that can be allocated by a zone.
See rctladm(1M) and setrctl(2) for information about using resource
controls.
Aug 14, 2006 SEMGET(2)
