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(5) for descriptions of the following attributes:


+--------------------+-----------------+
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
+--------------------+-----------------+
|Interface Stability | Standard |
+--------------------+-----------------+

SEE ALSO


ipcrm(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.


August 14, 2006 SEMGET(2)