======Install APC======
we need the pecl command so we can download and install APC from the repositories. 
  * use yum to install pecl
<code>
yum install php-pear php-devel httpd-devel
</code>

  * install APC
<code>
pecl install apc 
</code>
at the end you can read
<file>
Build process completed successfully
Installing '/usr/lib/php/modules/apc.so'
install ok: channel://pecl.php.net/APC-3.0.19
configuration option "php_ini" is not set to php.ini location
You should add "extension=apc.so" to php.ini
</file>
open php.ini, find
<file>
;;;;;;;;;;;;;;;;;;;;;;
; Dynamic Extensions ;
;;;;;;;;;;;;;;;;;;;;;;
</file>
add this line under it
extension=apc.so
save & exit, and restart the service
<code>
/etc/init.d/php_cgi restart
</code>
for apache
<code>
/etc/init.d/httpd restart
</code>