semget(2)

NAME

semget − get set of semaphores

SYNTAX

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

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

DESCRIPTION

The semget system call returns the semaphore identifier associated with key. A semaphore identifier and associated data structure and set containing nsems semaphores are created for key if one of the following are true:

The key is equal to IPC_PRIVATE

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

For further information, see intro(.).

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

The 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.

The sem_nsems is set equal to the value of nsems.

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

RETURN VALUE

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

DIAGNOSTICS

The semget system call will fail if one or more of the following are true:

[EINVAL] The 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 as specified by the low-order 9 bits of semflg would not be granted. For further information, see errno(.).

[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 ) & (semflg & IPC_EXCL )) is "true".

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