check_snmp_memory.pl

This plugin provides memory statistics data from NetSNMP and calculates percentage of used data based on amount of system/user memory as opposed to also including buffer/cache by default as other plugins do (which is a problem for heavily used servers where disk cache would end up using all unused memory).

The returned data are:
total_free - Total free memory in MB,
total_real - Total real memory on a system,
avail_real - Free real memory
total_swap - Total swap
avail_swap - Free swap memory
shared - In use shared memory (should be 0 on > 2.4 linux kernel)
buffer - In use buffer memory
cached - In use disk cache memory
total - Total memory on the system, real + swap
used_swap - Swap memory in use
%avail_real - Percent of available real memory
%used_real - Percent of real memory in use
%avail_swap - Percent of swap memory available
%used_swap - Percent of swap memory in use
user - Memory used by user (and system and kernel) processes
%user_real - Percent memory used for user processes in relation to total real memory (can be >100%)
%cached_real - Percent of user disk cache in relation to total real memory
%buffer_real - Percent of buffer memory in relation to total real

The plugin also serves as an example of using check_snmp_attributes plugin base library which does all the work where as plugin check_netsnmp_memory.pl file only defines RPL expressions used to calculate above from retrieved SNMP data.

There are also pretty and quite useful graph templates available for nagiosgrapher and pnp4nagios for performance data returned by this plugin.