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 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”. 

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. 

semget fails if one or more of the following are true:

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

[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. 

[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. 

[ENOSPC] A semaphore identifier is to be created but the system-imposed limit on the maximum number of allowed semaphores system wide would be exceeded. 

[EEXIST] A semaphore identifier exists for key but ((semflg & IPC_CREAT) and (semflg & IPC_EXCL)) is “true”. 

SEE ALSO

intro(2), semctl(2), semop(2). 

DIAGNOSTICS

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. 

September 02, 1992