linux-meminfo.rb

#!/usr/bin/env ruby
#
# linux-meminfo
#
#     by Eric Lindvall <eric@5stops.com>
#
# Gather more useful memory statistics for SNMP
#
# To see the example output, run:
#    linux-meminfo.rb -g .1.3.6.1.4.1.2021.4.6.0
#

# Add some debugging to help diagnose problems
if ARGV[0] == '-d'
  debug = true
  ARGV.shift
  require 'syslog'
  Syslog.open File.basename($0)

  Syslog.warning "Running with arguments: #{ARGV.inspect}"
end

# The numeric version of "UCD-SNMP-MIB::memAvailReal"
# You can find this by running:
#    snmptranslate -On UCD-SNMP-MIB::memAvailReal
OID_BASE = ".1.3.6.1.4.1.2021.4.6"

mem_info = {}

IO.foreach("/proc/meminfo") do |line|
  if m = line.chomp.match(/^(\w+):\s+(\S+)/)
    mem_info[m[1]] = m[2].to_i
  end
end

# The real free memory not counting buffers and caches as used
mem_free = mem_info['MemFree'] + mem_info['Buffers'] + mem_info['Cached']

# We only want to return this info if we're doing an snmpwalk to get this
# or doing an snmpget directly to the OID
case ARGV
when ['-n', OID_BASE], ['-g', "#{OID_BASE}.0"]
  puts "#{OID_BASE}.0"
  puts "integer"
  puts mem_free
  Syslog.warning "mem_free: #{mem_free}" if debug
end

snmpd.conf

# Override UCD-SNMP-MIB::memAvailReal to give useful statistics by using
# the net-snmp "pass" directive.
#
# We want to change the priority to make sure this gets used.
pass -p 5 .1.3.6.1.4.1.2021.4.6 /usr/share/snmp/linux-meminfo.rb

# If you want to print debug info to syslog:
#pass -p 5 .1.3.6.1.4.1.2021.4.6 /usr/share/snmp/linux-meminfo.rb -d