Thanks for getting back to me.
I can't find anything related to moodle in the logs and the result of munin-run are "Unknown service".
$ sudo munin-run moodle_users_online
# Unknown service 'moodle_users_online'
I checked file ownership and permissions and can't see a problem.
These are my first munin plugins written in php - could there be some dependencies I am missing?
Or perhaps I am missing something else - my munin configuration is as it comes out the box... I enabled the plugins by creating a symbolic link to the files, eg.
$ sudo ln -s /usr/share/munin/plugins/moodle_users_online.php /etc/munin/plugins/moodle_users_online.php
Is there anything else I should do?
Also, I confess I am not familiar with GIT and could not locate a download link - so I copied the code, pasted it into an editor and carefully followed the naming convention... Perhaps something went wrong here?
In the absence of logs I'm stumped...