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I am trying to generate a memory utilisation report for couple of Linux servers. I want to collect the % memory utilisation of servers for every 10 mins and I think sar can help to get that data. Earlier I though column %memused will directly give the % memory utilisation of the server. But after reading couple of articles I am suspecting that this not the correct memory utilisation of the server and therefore I want to know the best way to calculate the memory utilisation of the server.

Can anyone help me to calculate % memory utilisation of the server for every 10 mins using sar report or any other best to get the % memory utilisation.

06:39:47 PM kbmemfree kbmemused  %memused kbbuffers  kbcached  kbcommit   %commit
06:39:48 PM    616552   3307708     84.29    245368   2174816   1196772     24.07
06:39:49 PM    616552   3307708     84.29    245368   2174816   1196772     24.07
Alexander Volok
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Kaustubh Dhavale
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2 Answers2

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To calculate free memory value with SAR, use the below formula:

kbmemfree + kbbuffers + kbcached = actual free memory on the system

Using your example:

616552 + 245368 + 2174816 = 3036736KB

That’s around 2.89GB free memory.

I believe then you can subtract from total memory available to get the utilization.

João Fonseca
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The actual free memory on the system is free+buffers+cached. Buffers and cached are used to improve the system performance but will be returned to the free pool when needed.

If you are using a lot of shared memory (e.g mmaping a big cache) the calculation is slightly different and I use free for that

xxx@xxx:$ free -h
              total        used        free      shared  buff/cache   available
Mem:            62G        4.4G        7.9G         11G         50G         45G
Swap:          2.0G         12M        1.9G

The free memory in this case is:

  • (free + buff/cache) - shared.
  • 7.9 + 50 - 11
James Harvey
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