Tag: snmp

I’ve been using MRTG and routers2.cgi for years to graph the various aspects of a server that warrant monitoring. I’ve long known that they used something called rrdtool to do… well, something, but never had a need or desire to figure out exactly what that was.

But, having just moved my site to a new server, I was curious how the server would handle the load. Rather than setting up some behemoth like Nagios or Zabbix, which are full monitoring/alerting suites, I just wanted graphing. As I said, in the past I’ve used MRTG or routers2.cgi for this but both of them were overkill for me in this case. Since both of them used rrdtool, I figured that was a good place to look.

The two metrics I want to record are server load and in/out bandwidth. The first step is to create the RRDs (round robin databases). This was done via these commands:

# rrdtool create /mrtg/load.rrd --start N DS:load1:GAUGE:600:0:100 DS:load5:GAUGE:600:0:100 DS:load15:GAUGE:600:0:100 RRA:AVERAGE:0.5:2:800

# rrdtool create /mrtg/eth1.rrd --start N DS:in:COUNTER:600:0:10000000000 DS:out:COUNTER:600:0:10000000000 RRA:AVERAGE:0.5:2:800

A good explanation of what these various fields mean is here. In short, each “DS:” section defines a “column” (for fellow RDBMS users) in the database. The first one has 3 “columns,” named load1, load5, load15, each of which will contain GAUGE data. The second one contains two COUNTER fields, representing the bytes in/out for interface eth1.

To actually get the data I poll snmpd via this bash script:

#!/bin/bash

rrdupdate /mrtg/load.rrd N:
`/usr/bin/snmpget -v 2c -c public -Oqv localhost laLoad.1`:
`/usr/bin/snmpget -v 2c -c public -Oqv localhost laLoad.2`:
`/usr/bin/snmpget -v 2c -c public -Oqv localhost laLoad.3`

rrdupdate /mrtg/eth1.rrd N:
`/usr/bin/snmpget -v 2c -c public -Oqv localhost ifInOctets.3`:
`/usr/bin/snmpget -v 2c -c public -Oqv localhost ifOutOctets.3`

I have that run every 5 minutes via cron. Then to generate the actual graph, I run this script via cron:

#!/bin/bash

rrdtool graph /var/www/html/graphs/load.png 
        -N 
        -E 
        --start now-30hours 
        --title "Load Averages" 
        --width 300
         --x-grid MINUTE:60:HOUR:2:HOUR:4:0:%H
        --height 200 
        -u 1.0 
        --lower-limit 0
        --vertical-label "Load Avg" 
        --full-size-mode 
-a PNG --title="Load Avg" 
'DEF:load1=/mrtg/load.rrd:load1:AVERAGE' 
'VDEF:load1last=load1,LAST' 
'DEF:load5=/mrtg/load.rrd:load5:AVERAGE' 
'DEF:load15=/mrtg/load.rrd:load15:AVERAGE' 
'AREA:load15#33CC33:15 Min Load Avg ' 
'LINE1:load1#0000ff:1 Min Load Avg ' 
'GPRINT:load1:AVERAGE:"Load1 Avg:%3.2lf"' 
'GPRINT:load1last:Drawn at %Y-%m-%d, %H:%M:strftime' 
#'LINE1:load5#ff00ff:5 Min Load Avg ' 

 
rrdtool graph /var/www/html/graphs/eth1.png 
        -N 
        -E 
        --start now-30hours 
        --title "eth1 traffic" 
        --width 300
         --x-grid MINUTE:60:HOUR:2:HOUR:4:0:%H
        --height 200 
        -u 1000000 
        --lower-limit 0
        --vertical-label "bps" 
        --full-size-mode 
-a PNG --title="eth1 traffic" 
'DEF:eth1in=/mrtg/eth1.rrd:in:AVERAGE' 
'CDEF:eth1inbits=eth1in,8,*' 
'VDEF:eth1last=eth1in,LAST' 
'DEF:eth1out=/mrtg/eth1.rrd:out:AVERAGE' 
'CDEF:eth1outbits=eth1out,8,*' 
'AREA:eth1inbits#33CC33:eth1 in ' 
'LINE1:eth1outbits#0000ff:eth1 out' 
'GPRINT:eth1last:Drawn at %Y-%m-%d, %H:%M:strftime' 

The final graphs look decent, though not very fancy, but I’ll play around with it a bit more: