I just got an email with the subject line:

Cron <root@server> /usr/bin/mrtg /etc/mrtg/mrtg.cfg

and message:

ERROR: I guess another mrtg is running. A lockfile (/etc/mrtg/mrtg.cfg_l) aged 0 seconds is hanging around. If you are sure that no other mrtg is running you can remove the lockfile

around the same time, server load spiked to 180 for about a minute.

no idea what happend, or what it means. anyone got any ideas?

Your mrtg tried to run when a mrtg process was already running.

what does mrtg do, and how can i fix it?

http://people.ee.ethz.ch/~oetiker/webtools/mrtg/mrtg.html