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Tunable Kernel Parameters
HP-UX 11i Version 3: February 2007

Technical documentation

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sema — enable or disable System V IPC semaphores at boot time


The sema tunable is obsolete. The System V IPC semaphore subsystem is always enabled.


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.


Installation of optional kernel software, from HP or other vendors, may cause changes to tunable parameter values. After installation, some tunable parameters may no longer be at the default or recommended values. For information about the effects of installation on tunable values, consult the documentation for the kernel software being installed. For information about optional kernel software that was factory installed on your system, see HP-UX Release Notes at http://docs.hp.com.


sema was developed by AT&T.

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