semget(2) SYSTEM CALLS semget(2)
NAME
semget - get set of semaphores
SYNOPSIS
#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/sem.h>
int semget(keyt key, int nsems, int 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 IPCPRIVATE.
key does not already have a semaphore identifier asso-
ciated with it, and (semflg&IPCCREAT) is true.
On creation, the data structure associated with the new
semaphore identifier is initialized as follows:
semperm.cuid, semperm.uid, semperm.cgid, and
semperm.gid are set equal to the effective user ID and
effective group ID, respectively, of the calling pro-
cess.
The access permission bits of semperm.mode are set
equal to the access permission bits of semflg.
semnsems is set equal to the value of nsems.
semotime is set equal to 0 and semctime 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 speci-
fied 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 associ-
ated with it is less than nsems, and nsems is
not equal to zero.
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semget(2) SYSTEM CALLS semget(2)
ENOENT A semaphore identifier does not exist for key
and (semflg&IPCCREAT) is false.
ENOSPC A semaphore identifier is to be created but
the system-imposed limit on the maximum
number of allowed semaphore identifiers sys-
tem 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
both (semflg&IPCCREAT) and (semflg&IPCEXCL)
are both true.
SEE ALSO
intro(2), semctl(2), semop(2), stdipc(3C).
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.
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