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IPCS Shared Memory, Message Queues and Semaphores

Those important parameters are described in each man page and on thousands of web pages.
We hope that our two graphics make it more easy to understand them.

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IPCS Message Queues

View full size IPCS Message Queues

IPCS Shared Memory

View full size IPCS Shared Memory ipcs -qa displays information about IPCS-Queues

ipcs -qa |grep -v "0 0" lists only IPCS-Queues which have waiting messages (There are 5 spaces between "0 0")

A value "1" for QNUM means, that there is one message waiting behind that message which is currently being processed (active); that means that there are indeed 2 messages in that queue.

ipcs -aq -D0 ("D-Zero") prints content of the message queues

IPCS Semaphores



Number of semaphore identifiers


Number of semaphores in system


Maximum number of semaphores per ID


Number of undo structures in system

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