Monitoring free memory via SNMP

kirukan · 08-29-2014, 02:32 AM

Hi Guys,
What is the industry practice/standard to monitor the free memory in linux?
I know mostly people are using "memTotalFree" snmp oid and set threshold to generate traps.
But in some situation this memTotalFree is very low and it doesn't mean that the system is running out of memory. so what we need to confirm is free real memory/physical free memory via "free" command. if we see we have enough physical free memory and swap usage zero then we can confirm that the system is healthy.

However, some poor customers are worrying about the memory alerts. in this situation how you explain/educate the customers?

Thanks.

Habitual · 08-29-2014, 07:30 AM

http://www.debianadmin.com/linux-snm...tatistics.html
may help.

kirukan · 08-30-2014, 01:41 AM

Thanks for your link,

Quote:

(Used – buffers – cached) / Total * 100 = % memory used

So you could get the following (expressed as Perl code):

my $memRealTotalOID = '.1.3.6.1.4.1.2021.4.5.0';
my $memRealAvailOID = '.1.3.6.1.4.1.2021.4.6.0';
my $memRealBuffersOID = '.1.3.6.1.4.1.2021.4.14.0';
my $memRealCachedOID = '.1.3.6.1.4.1.2021.4.15.0';
# Memory Calculations
my $memRealUsed = $memRealTotal - $memRealAvail;

Then you can alert on % RAM used:

my $realPercent = (($memRealUsed - $memRealBuffers - $memRealCached )/ $memRealTotal) * 100;

This is fine to alert real/physical used memory percentage but if i am not mistaken mostly systems are designed to send traps for memTotalFree. why? any special reason/industry practice?
There are some debates, which is best practice to alert for memory? memTotalFree or RealFree
OR
Send traps for both, case closed!!