PHP Startup: Unable to load dynamic library '/usr/lib/php5/20100525/apc.so'

If you are not planning to use APC then this can be safely removed from your PHP configuration.

First, find your php.ini file and edit it.

Find "apc" in the php.ini file, you should find a line that looks like this:

extension=apc.so

You can comment out this line by adding a semi-colon in front, e.g.

;extension=apc.so

If you cannot find the "apc.so" reference in your php.ini file, it could be included in a separate file. You could locate it by searching for the string "apc.so" within all files on your server, it must be there somewhere!

Just comment out that line then restart Apache.

APC is no longer compatible with PHP, as of PHP 5.5 (this may apply to 5.4 as well, I can't find the specific document right now). However Zend OPCACHE is included (in 5.5, no install necessary), because of this APC has been removed from PECL. Take a look at installing Zend OPCACHE instead. http://php.net/manual/en/opcache.installation.php

Depending on what you are running you may not need an opcode cache, however sites like wordpress, drupal, joomla, etc often benefit from having it.