The log file does not have graph data in it. The log file can be deleted as needed.
The /etc/nagiosgraph/map file contains the regular expressions used to parse the data received. I suspect that these values are being parsed by the default rule, but they need custom rules.
Nagiosgraph doesn't delete data files, so something else did, or the configuration changed.
You can look in the "Customizing the Graphs" section of the readme, to see if there's...
That is a consequence of using rrdtool for storage. It decides how to store and present...
No. You could use rrdtool's dump option to export the data, but there is no functionality...
The default map file has a pattern for PROCS.*?(\d+) processes\n which looks like...
Use the testentry.pl tool to validate the output from the commands with the map file...