System Calls semget(2)
semget - get set of semaphores
int semget(key_t key, int nsems, int semflg);
The semget() function returns the semaphore identifier asso-
ciated 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:
o key is equal to IPC_PRIVATE.
o key does not already have a semaphore identifier asso-
ciated with it, and (semflg&IPC_CREAT) is true.
On creation, the data structure associated with the new
semaphore identifier is initialized as follows:
o 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
o The access permission bits of sem_perm.mode are set
equal to the access permission bits of semflg.
o sem_nsems is set equal to the value of nsems.
o sem_otime is set equal to 0 and sem_ctime is set equal
to the current time.
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.
The semget() function will fail if:
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.
SunOS 5.9 Last change: 30 Nov 1993 1
System Calls semget(2)
A semaphore identifier exists for key but both
(semflg&IPC_CREAT) and (semflg&IPC_EXCL) are both
The nsems argument is either less than or equal to 0
or greater than the system-imposed limit; or a sema-
phore 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.
A semaphore identifier does not exist for key and
(semflg&IPC_CREAT) is false.
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
When a UFS file system is mounted with logging enabled, file
system transactions that free blocks from files might not
actually add those freed blocks to the file system's free
list until some unspecified time in the future. This
behavior improves file system performance but does not con-
form to the POSIX, Single UNIX Specification, SPARC Confor-
mance Definition, System V Application Binary Interface,
System V Interface Definition, and X/Open Portability Guide
Standards, which require that freed space be available
immediately. To enable standards conformance regarding file
deletions or to address the problem of not being able to
grow files on a relatively full UFS file system even after
files have been deleted, disable UFS logging (see
ipcrm(1), ipcs(1), mount_ufs(1M), intro(2), semctl(2),
SunOS 5.9 Last change: 30 Nov 1993 2