Here is how to install Memcache for PHP on a CentOS 6 cPanel / WHM box. Some of the guides suggest that you need libevent (well, you do need libevent), though when I tried it, I already had it installed. But if you need it, yum will sort you out.
yum install libevent
Next, install memcache itself. Note that the package is called memcached.
yum install memcached
Of course, just installing it doesn’t mean that the daemon is running. So don’t forget to start it too!
Finally, we need to add the PHP extension. Beware that the PECL installer on WHM won’t work! So you need to compile it manually from source. That isn’t too difficult though.
wget http://pecl.php.net/get/memcache tar zxvf memcache cd memcache-3.0.6 phpize ./configure make make install
And add the extension to your php.ini.
Now restart Apache and a memcache section should appear in your PHP info.