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:
eth1 graph
load graph
