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I am using top command on my centos server.

Mem:   8055100k total,  3832228k used,  4222872k free,    57968k buffers

Swap:  8191992k total,        0k used,  8191992k free,  3574740k cached

In case of memory, I see 3832228k used, but when I check per process consumption, its showing 0%. can some one tell which process is consuming this memory.

I have also attached a screenshot for this.enter image description here

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closed as off topic by Thomas W., qbi, Seth, Eliah Kagan, Jorge Castro Feb 7 '13 at 4:37

Questions on Ask Ubuntu are expected to relate to Ubuntu within the scope defined by the community. Consider editing the question or leaving comments for improvement if you believe the question can be reworded to fit within the scope. Read more about reopening questions here. If this question can be reworded to fit the rules in the help center, please edit the question.

According to the FAQ, Ask Ubuntu provides support for recognized Ubuntu flavors. Your question may be welcome at Unix & Linux Stack Exchange –  user25656 Feb 6 '13 at 5:15
It appears you're using Ubuntu as an SSH client to access your CentOS server. Since the issue is with the CentOS server, this is off-topic; as @vasa1 says, you should ask this somewhere CentOS is supported. –  Eliah Kagan Feb 7 '13 at 0:30

1 Answer 1

From http://www.linuxquestions.org/questions/linux-newbie-8/top-used-memory-vs-ps-processes-memory-782765/

The "used" memory reported by top includes "buffers" and "cached", which are categories of memory use that are not included in any individual process in ps. The whole topic is more complex than you might expect. But if you want a nearly correct greatly simplified view, you should consider "buffers" and "cached" to be free memory. So the actual free memory is the sum of what top reports as "free", "buffers" and "cached". The actual used memory is what top reports as "used" minus both "buffers" and "cached" The free command gives you used and free values both before and after that adjustment. top only gives you the unadjusted values.

Buffers and caches are set aside for processing data. Even though they might not genuinely be "used" at any given moment, top reports those buffers and caches used anyway since they are set aside for use. So that memory is technically "used" even though it is might not actively be used.

Reserved might be a better word for the memory "used" by buffers and caches when there is nothing in them.

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