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ipcrm

Now that you identified the shared memory and other IPC metrics, what do you do with them? You saw some usage earlier, such as identifying the shared memory used by Oracle, making sure the kernel parameter for shared memory is set, and so on. Another common application is to remove the shared memory, the IPC message queue, or the semaphore arrays.

To remove a shared memory segment, note its shmid from the ipcs command output. Then use the –m option to remove the segment. To remove segment with ID 3735562, use:

# ipcrm –m 3735562

This will remove the shared memory. You can also use this to kill semaphores and IPC message queues as well (using –s and –q parameters).

Usage for Oracle Users
Sometimes when you shutdown the database instance, the shared memory segments may not be completely cleaned up by the Linux kernel. The shared memory left behind is not useful; but it hogs the system resources making less memory available to the other processes. In that case, you can check any lingering shared memory segments owned by the “oracle” user and then remove them, if any using the ipcrm command.

 
(Extracted from oracle technet notes author Arup Nanda)