When I first installed munin on my machine, I was getting errors like:

Terminating process. at /usr/share/perl5/Munin/Master/UpdateWorker.pm line 139

After some searching online, I found out that this was because it doesn’t like capital letters in the hostname. So, to fix this error, you need to make your hostname ALL LOWERCASE in both the munin-node.conf file of your client, and the host structure tree of your munin.conf file.

A side-effect of this problem was getting 403 forbidden errors when trying to access my munin directory – this is because the apache.conf file that munin comes with on (for debian, at least) does not have indexes enabled, and because as a result of the hostname capitalisation issue, no html files are being generated by munin. A combination of these two things results in the aforementioned 403 errors.

I hope that this has helped someone – I know that I could have done with reading this post three days ago :).