Linux Question

[Hugo van der Kooij]

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Thomas Guyot-Sionnest wrote:
> On 22/08/08 10:46 AM, Edwin Zoeller wrote:
>> We have recently installed Redhat AS4 throughout our network. I have
>> installed various plugins from the Nagios Exchange site for Linux and
>> all seems to be well, except for the check_ram command. I am running
>> this on various servers with different configurations and all are giving
>> the same results. Here is what I have on one of the servers:
> 
>> check_ram -n -w 20MB -c 10MB ( the system has 8GB installed), results
>> display 30MB free (am I doing this right?)
> 
>> Other admins here are disputing the results and claim that Linux buffers
>> all the memory and gives what it needs. I don't know for fact it this is
>> true. I have also run top, free and ps -eo checking on memory size, all
>> give back the same results as the Nagios plugin. Is this plugin with the
>> option chosen giving real memory results or bogus results.
> 
>> My question, in desperation, can anyone explain in very simple terms how
>> Linux memory works? Also how are you monitoring memory, using what
>> command and how it is configured etc.
> 
> All unused memory gets buffered/cached eventually if your server is
> doing I/0. I've seen very stable servers with 32GB get down to only a
> few MBs free, but the picture is much better if you account the
> buffered/cached memory which for most of it can be freed anytime if needed.
> 
> For that reason you should add the buffer/cache memory to the total
> (i.e. the "-/+ buffers/cache:" line of the "free" command).
> 
> My check_memory script does that. it's written in Perl and uses the
> Nagios::Plugin Perl module (available on CPAN).
> 
> http://www.nagiosexchange.org/cgi-bin/page.cgi?g=1433.html;d=1

The whole point of this is that unused memory is wasted memory. So if
you do not use RAM for aplications itself your system will find a good
use for it to speed up the system by using it for buffers and cache.

Hugo.

- --
hvdkooij at vanderkooij.org               http://hugo.vanderkooij.org/
PGP/GPG? Use: http://hugo.vanderkooij.org/0x58F19981.asc

	A: Yes.
	>Q: Are you sure?
	>>A: Because it reverses the logical flow of conversation.
	>>>Q: Why is top posting frowned upon?

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