NAME
sema — enable or disable System V IPC semaphores at boot time
VALUES
Allowed values
1 (on)
or
0 (off)
DESCRIPTION
The
sema
tunable is a "switch" designed to enable the entire System V (InterProcess
Communications package (IPC) semaphore subsystem.
It not only allows user access, but when disabled, no memory space will even be
reserved on system boot, and the System V IPC semaphore subsystem will be
totally removed.
Since some system daemons require use of these semaphores, a disabled
semaphore system will be the exception.
Overview
System V IPC is comprised of mechanisms for arbitrary processes to send and
receive data messages, share virtual address space and use semaphores
to synchronize execution.
A System V semaphore is a synchronization method for user processes to
synchronize or serialize access to common data and resources.
Each semaphore "set" has an ID, but each set can contain one or more
independent semaphores.
Semaphore sets are created or initially accessed
through
semget()
using an application-specified "key", which can be generated by
ftok().
Operations on the set are performed through
semop()
and
semctl().
Semaphore sets are removed through
semctl()
or the
ipcrm
command.
Who Is Expected to Change This Tunable?
Anyone.
Restrictions on Changing
Changes to this tunable take effect at the next reboot.
What Are the Side Effects of Turning the Tunable Off?
Memory space will
not
be reserved on system boot, and the System V IPC semaphore subsystem will
be totally removed.
As some system daemons may require use of these semaphores, turning
this tunable off may cause some other system services to be unavailable.
What Other Tunable Values Should Be Changed at the Same Time?
All the System V semaphore tunables are interrelated and should
not
be treated as independent variables.
The tunables must be evaluated as a system to ensure they
reflect the application requirements.
The
sema
tunables include
semaem,
semmap,
semmni,
semmns,
semmnu,
semmsl,
semume,
semvmx,
and
sysv_hash_locks.
WARNINGS
All HP-UX kernel tunable parameters are release specific.
This parameter may be removed or have its meaning changed in
future releases of HP-UX.
AUTHOR
sema
was developed by AT&T.
SEE ALSO
ipcs(1),
ipcrm(1),
semget(2),
semop(2),
semctl(2),
semaem(5),
semmap(5),
semmni(5),
semmns(5),
semmnu(5),
semmsl(5),
semume(5),
semvmx(5),
sysv_hash_locks(5).
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