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SEMGET(2) System Calls Manual SEMGET(2)

get semaphore set

#include <sys/sem.h>
semget(key_t key, int nsems, int semflg);

The semget() system call returns the semaphore identifier associated with key.
A new set containing nsems semaphores is created if either key is equal to IPC_PRIVATE, or key does not have a semaphore set associated with it and the IPC_CREAT bit is set in semflg.
The access modes of the created semaphores is specified in semflg as a bitwise OR of zero or more of the following values:
SEM_A        alter permission for owner 
SEM_R        read permission for owner 
SEM_A >> 3   alter permission for group 
SEM_R >> 3   read permission for group 
SEM_A >> 6   alter permission for other 
SEM_R >> 6   read permission for other
If a new set of semaphores is created, the data structure associated with it (the semid_ds structure, see semctl(2)) is initialized as follows:

semget() returns a non-negative semaphore identifier if successful. Otherwise, -1 is returned and errno is set to reflect the error.

The caller has no permission to access a semaphore set already associated with key.
Both IPC_CREAT and IPC_EXCL are set in semflg, and a semaphore set is already associated with key.
nsems is less than or equal to 0 or greater than the system limit for the number in a semaphore set.
A semaphore set associated with key exists, but has fewer semaphores than the number specified in nsems.
A new set of semaphores could not be created because the system limit for the number of semaphores or the number of semaphore sets has been reached.
was not set in semflg and no semaphore set associated with key was found.

semctl(2), semop(2), ftok(3)
November 15, 2014 OpenBSD-5.9