Dongle Blog

I finally got round to installing cacti last week.

I’ve used MRTG fairly extensively. It does a pretty good job but has a few limitations. Perhaps the most obvious is that it’s not particularly pleasant to configure. You have to edit text files manually specifying each snmp oid to monitor, it’s fairly hard to get started and the only way to reuse templates is via cut & paste. It’s not too hard to get some basic graphs but I found getting things looking really nice tended to take a lot of effort. Another big problem is the overhead of the poller; with a medium sized network it’s quite easy to find that the poller hasn’t finished the previous run when it gets started again.

RTG adds some interesting features; the poller is written in C and much faster, also the graphs are plotted as they are displayed making the web interface slightly slower but meaning the machine isn’t tied up producing hundreds of graphs for each cycle (which will probably never be viewed). Another advantage of this is that it is possible to configure the desired time range for the graphs as they are produced rather than just the four (daily, weekly, monthly, annual) which MRTG gives by default. This is a nice feature, but I didn’t actually find it all that useful; but it would useful for ISPs etc who need to make accurate historical measurements of bandwidth.

When I started at my current job, getting some service monitoring up and running was a priority and Nagios was the obvious choice. Getting some trend monitoring was a lower priority. I had intended to try Cricket which I’d heard good things about, but came across Cacti.

Cacti uses RTG to actually plot the data, but provides it’s own SNMP poller, written in C, making it much quicker than MRTG. More significantly it has a very nice web interface which lets you easily, for example, add a host, get a list of network interfaces and choose some of these to produce graphs.