Linux – Memory usage on SunOS and Linux

linuxmemorysolaris

I have some doubts with memory usage.
Currently I have nagios check who measures used memory from free -m command on Linux. I added another script for memory usage from http://exchange.nagios.org/directory/Plugins/Operating-Systems/Solaris/check_mem-2Epl/details and it measures for Solaris from vmstat and for Linux from /proc/meminfo, with this new check a have a lot more usage 20 % – 30 % more on some hosts.

./check_mem.pl -f -w 90 -c 60
CRITICAL - 34.6% (439872 kB) free!|TOTAL=1272376KB;;;; USED=832504KB;127237;508950;; FREE=439872KB;;;; CACHES=418977KB;;;;

this is output from new script on Solaris host
on this host I also have 

    vmstat 1 2
 kthr      memory            page            disk          faults      cpu
 r b w   swap  free  re  mf pi po fr de sr s0 -- -- --   in   sy   cs us sy id
 0 0 0 1184172 474856 54 222 0  0  0  0 112 8  0  0  0  231 1735  669  1  8 91
 0 0 0 1175352 440948 16 58  0  0  0  0  0  0  0  0  0  229   83  190  0  3 97

values from vmstat and from new script are OK. I mean the script collects from vmstat values ok.
I need to know what is the best way to measure memory usage on Solaris and Linux, how can I see how much OS uses and how much is used by app is it vmstat(Sunos) and /proc/meminfo (Linux) OK for that?

Best Answer

vmstat is not that useful to measure memory usage. It doesn't give any metric quantifying how much virtual and physical memory is used and what is using it. It is however a very good tool to measure RAM shortage. You just need to monitor the sr column (scan rate). As long as it stays equal to zero, you shouldn't worry about RAM. If it is not equal to zero, you should investigate what is demanding RAM.

To have a detailed idea about what is using your system memory, in addition to the already suggested echo ::memstat | mdb -k command, you can run prstat -n 1 -a which will give you the memory usage per user, prstat -n 1 -Z for zone usage and prstat -s rss for per process usage sorted by RAM.

In prstat output, the SWAP column shows the virtual memory used and the RSS column, the RAM used.

About kernel usage, you can run kstat -n system_pages and have a look to the pp_kernel value.

To precisely answer to your question:

how can I see how much OS uses and how much is used by app is it vmstat(Sunos) and /proc/meminfo (Linux) OK for that?

No vmstat is not OK for that on Solaris. You might run echo ::memstat | mdb -k and parse its output.

The sum of the lines "Anon" and "Exec and libs" is the RAM used by applications, The line "Kernel" reports the RAM used by the kernel, the lines "ZFS ...", "Page cache" and "Free (cachelist)" show RAM used to cache data and the line "Free (freelist)" reports unused, i.e. wasted RAM.

Note: all of the above is about Solaris.

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