I’ve been working on getting a mapnik server up and running and tweaked the way I want. Here are some useful things I learned.

Showing logs for renderd
tail -f /var/log/syslog | grep renderd

Restarting the renderd process
/etc/init.d/renderd restart

This is the default maps view file. You need to edit it to change the server address from localhost to (for example) your external IP, so you can view the maps over network.
nano /var/www/osm/slippymap.html

This is where you can find configuration XML files
cd /etc/mapnik-osm-data/

This is the config file that lists the shape files in use
layer-shapefiles.xml.inc

This is where the shape file data is stored
/usr/share/mapnik-osm-data/

Clear all cached tiles
rm -Rf /var/lib/mod_tile/default