I just stumbled upon an error in one of my clients web spaces.

The costumer is running a presta shop on his web space and encoured an error in form of the „white screen of death“. While taking a look to the server logs I encountered a repeating error about

[Mon May 05 22:34:06 2014] [warn] mod_fcgid: stderr: PHP Fatal error:
Call to undefined function apc_cache_info() in /client/CacheApc.php on line xy

This error is caused by a missing extension „apc.so“. So in his case, the APC was disabled in his web settings.

It can be enabled in the php.ini (/etc/php5/apache2/php.ini on an Ubuntu system) by adding the following lines:

# apc
apc.shm_size = 128 #actual size of the cache -
#depends on your server ram. For a small shop, this would be pretty much enough