Centos is one of the great network operating systems, it was developed by a group of people who saw Red Hat Enterprise version 4 had become super reliable but slightly bloaty, they exercised their rights under the GNU public license got the source of RHEL4, put it on a stairmaster and gave it to the people.
Likewise Nagios is a great open source network monitoring system, if you are a Linux user and run a network chances are you will have come across Nagios, short of forking out about £1000 it is in fact pretty much your only option. About 12 months ago I installed Nagios on Fedora and it was a breeze, even though Nagios is a very comprehensive system requiring lots of fiddly configuration, on Fedora if you follow the instructions you will succeed in getting going in about an hour.
Unfortunately given that Centos and Fedora have a common ancestry and are very similar, trying to install Nagios on Centos will drive you up the wall. Unless I have done something stupid without realising it, installing the system from RHEL4 RPM's seems to scatter the files from one end of the disk to the other and it takes lots of patience to track them all down and link everything up. My advice would be follow the instructions to the letter but if you don't find the files you are looking for don't be surprised. Click here for the main Nagios site, this post is not a guide to installing Nagios on Centos just an amendment to the install guide based upon my rather frustrating experience.
Just in case I forget or anyone else trips over this, the locations are as follows:
Config CFG files - /etc/nagios
Web interface files - /usr/share/nagios
Log files - /var/log/
CGI files - /usr/lib/nagios/cgi
A guy called Dag (??) has done some Centos RPM's but I couldn't subscribe to his repository, if you can it is quite possible that he has reworked the install to follow the instructions. Couldn't resist doing my 'Google Images' thing for Dag, turns out this Swedish guy is also comfortable going my the name Dag. There are some great translations for Dag on wikipedia, in Swedish it means 'Day' and in Turkish it refers to a 'Mountain'.
So now the dust has settled after our mammoth network rewire last week and Nagios is running sweetly I feel quite satisfied with everything. As expected we have had a few static routes crawl out of the woodwork and we have renewed our efforts to use DNS rather that IP addresses for routing around the network. It turns out reversing the VPN connections was not all that it promised and we have moved them all back again, it also seems that having Nagios running is actually very good for the stability of the VPN as the frequent pinging seems to keep the routers awake and the tunnels in good repair.
One job left to complete is to define a custom status map for Nagios, as we have over a hundred nodes on the network being monitored the auto generated map is a bit of a mess so I have to define the map by hand which is a bit of a pain. That said it will look very nice as we have purchased an icon library for our software development and their networking set is very sweet. See left for a sneak peek, note however that our main managed switches are not down it is just that Netgear have issued a firmware upgrade they are short of. One day I would love to do a more comprehensive Flash front-end to Nagios but frankly right now I have better things to do.
Another job I think would pay dividends would be to set up a secondary DNS server at Manchester, it is probably quite straight forward but I think I will let the dust settle before attempting this one.