Setup WordPress Permalinks (Pretty / Clean URLS) on Apache under Linux (Ubuntu):
Check for Apache Mod_ReWrite – Following lists all the loaded modules
sudo apache2ctl -M
Enable Mod_Rewrite
sudo ln -s /etc/apache2/mods-available/rewrite.load /etc/apache2/mods-enabled/rewrite.load
Restart Apache
sudo /etc/init.d/apache2 restart
Setup Permalinks in WordPress
/%monthnum%/%postname%
/. 