semget(2) (man pages section 2: System Calls)

man pages section 2: System Calls

semget(2)

NAME

semget– get set of semaphores

SYNOPSIS

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

key

nsems

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:

key is equal to IPC_PRIVATE.
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:

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 access permission bits of sem_perm.mode are set equal to the access permission 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.

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; or 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.