Transporting from GitHub:
Right now the system logs a few things. After an installation there is an installation log, and during the day all activity from dnsmasq is logged. In the default installation that logfile is purged, therefor the admin interface will only show ‘todays’ activity.
Would it be helpfull if there is a general logfile that is not overwritten and saves a few things? Think things like the weekly update of the adlists, the automatic update of the system, maybe even the daily statistics before the normal pihole log is flushed at the end of the day
(logfile flushed, results for 2016-02-16: xx queries, xx.xxx dns queries, xx % ads, on this day xx.xxx domains are blocked by pi-hole).
That way you can look back and see if things have indeed taken place. It would also allow for things like
pi-hole system upgraded from 2.5.2 to 2.5.3 on 2016-12-18 23:55 hrs.