SEMGET(2)

NAME
semget - get set of semaphores

SYNOPSIS
#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/sem.h>

int semget (key, nsems, semflg)
key_t key;
int nsems, semflg;

DESCRIPTION
semget returns the semaphore identifier associated with key.

A semaphore identifier and associated data structure and set containing nsems semaphores (see kedef(2)) are created for key if one of the following are true:

    key is equal to IPC_PRIVATE.

    key does not already have a semaphore identifier associated with it, and (semflg & IPC_CREAT) is ``true''.

Upon creation, the data structure associated with the new semaphore identifier is initialized as follows:

    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.

    The low-order 9 bits of sem_perm.mode are set equal to the low-order 9 bits of semflg.

    sem_nsems is set equal to the value of nsems.

    sem_otime is set equal to 0 and sem_ctime is set equal to the current time.

    The data structure associated with each semaphore in the set is not initialised. The function semctl with commands SETVAL or SETALL can be used to initialise each semaphore.

RETURN VALUE
Upon successful completion, a non-negative integer, namely a semaphore identifier, is returned. Otherwise, a value of -1 is returned and errno is set to indicate the error.

ERRORS
semget will fail if one or more of the following are true:

EACCES
    A semaphore identifier exists for key, but operation permission (see kedef(2)) as specified by the low-order 9 bits of semflg would not be granted.

EINVAL
    nsems is either less than or equal to zero or greater than the system-imposed limit.

EINVAL
    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 zero.

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 semaphore identifiers system wide would be exceeded.

EEXIST
    A semaphore identifier exists for key but ((semflg & IPC_CREAT) && (semflg & IPC_EXCL)) is ``true''.

SEE ALSO
kedef(2), semctl(2), semop(2).