Now I’ll talk about how to monitor virtual memory, on Linux (where it’s easy) and, next time, on Solaris (where most people and systems do it incorrectly.) Running programs that require more memory than the system has will mean pages (or processes) are moved to/from disk and memory in order to get enough physical memory to run – and system performance will suck.) (TL DR: swapping is moving an entire process out to disk paging is moving just specific pages out to disk, not an entire process.
One service is created on each host that provides the section creates a service instead.In a prior blog post, I talked about what virtual memory is, the difference between swapping and paging, and why it matters. Hint: If you want to monitor swapping, you probably better measure major pagefaults. That means that this check gets critical if the memory used by processes is twice the size of your RAM. So when defining a level to check against, the only value that is not affected by such internals of memory management is the total amount of virtual memory used up by processes (not by disk buffers).Ĭheckmk lets you define levels in percentage of the physically installed RAM or as absolute values in MB. That is because Linux has taken RAM from processes in order to increase disk buffers. It does this in situations where disk buffers (are assumed to) speed up the overall performance more than keeping rarely used parts of processes in RAM.įor example after a complete backup of your system you might experiance that your swap usage has increased while you have more RAM free then before. Linux tends to swap out parts of processes even if RAM is available. In fact it is the only way to do it right (at least for Linux): What parts of a process currently reside in physical RAM and what parts are swapped out is not related in a direct way with the current memory usage. You can define a warningĪnd critical level for the usage of virtual memory, This check measures the current usage of physical RAM and Check manual page of mem_used Usage of Physical and Virtual RAM
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