SEMGET(2) System Calls SEMGET(2)
NAME
semget - 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
following 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
identifier 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
semaphore 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 permission
(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
(
semflg&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
semaphores 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
(
semflg&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(7) for descriptions of the following attributes:
+--------------------+-----------------+
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
+--------------------+-----------------+
|Interface Stability | Standard |
+--------------------+-----------------+
SEE ALSO
ipcrm(1),
ipcs(1),
Intro(2),
semctl(2),
semop(2),
setrctl(2),
ftok(3C),
attributes(7),
standards(7),
rctladm(8)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(8) and
setrctl(2) for information about using resource
controls.
August 14, 2006
SEMGET(2)