SUSE Linux Enterprise Server - What Does the memlock Option in limits.conf Do?

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What does the memlock option in /etc/security/limits.conf do?

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The limits.conf file is the configuration file for the pam_limits module. The PAM module limits the system resources that a user process can acquire. Per the manpage for limits.conf, the memlock option is used to set the maximum amount of locked-in-memory address space as given in kilobytes:

memlock
maximum locked-in-memory address space (KB)

This is memory that will not be paged out. It is frequently used by database management applications such as Oracle or Sybase to lock shared memory for a shared pool so that it is always in memory for access by multiple sessions.

For example, huge pages are locked into physical memory and are allocated by database applications. Therefore, one must assure that memlock is set to account for the at least the total amount of huge pages that will be allocated.

Example settings:

Oracle	Soft	memlock	1048576
Oracle	Hard	memlock	1048576

To verify the memlock setting for a process, use the -l option with the ulimit command:

# ulimit -l
1048576

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