How do I change the Debug build to On in lamp stack environment?
As i said in the comments you need to enable display_errors
instead of Debug build.
Goto your php.ini
From terminal:
sudo gedit /etc/php5/apache2/php.ini
Search for the option display_errors
(not the already commented option, means jump to second search result)
Change from Off to On
display_errors = On
Also enable these options as well as you may need in future
display_startup_errors = On
log_errors = On