Zope can keep an event log, on the filesystem, which is very useful for troubleshooting problems. It's enabled by default in Zope 2.7, in INSTANCE_HOME/log/event.log .

If you lower the log priority threshold in INSTANCE_HOME/etc/zope.conf, you'll see more verbose logging.

Don't confuse this with the ErrorLog, which is in the ZODB. You can check a box there to have error tracebacks show up in the event log, which can be handy.

Zope 2.6 needs EVENT_LOG and EVENT_LOG_SEVERITY environment variables to control this.