Continuous backup of critical system files

[Maxim Khitrov]

Hello all,

I'm setting up a firewall using FreeBSD 7.2 and thought that it may
not be a bad idea to have a continuous backup for important files like
pf and dnsmasq configurations. By continuous I mean some script that
would be triggered every few minutes from cron to automatically create
a backup of any monitored file if it was modified. I also have a full
system backup in place that is executed daily (dump/restore to a
compact flash card), so the continuous backup would really be for
times when someone makes a mistake editing one of the config files and
needs to revert it to a previous state.

My initial thought was to create a mercurial repository at the file
system root and exclude everything except for explicitly added files.
I'd then run something like "hg commit -m `date`" from cron every 10
minutes to record the changes automatically. Can anyone think of a
better way to do this (existing port specifically for this purpose)?
Obviously, I need a way to track the history of a file and revert to a
previous state quickly. The storage of changes should be as
size-efficient as possible.

- Max