Before you consider installing APC you need to ensure your PHP handler is either set to DSO or FastCGI, as unfortunately suPHP is unsupported. For the best results consider running PHP as DSO + mod_ruid2 for optimal performance and security.
To install APC please run the following from SSH:
cd /usr/local/src
wget http://pecl.php.net/get/APC-3.1.8.tgz
tar -zxvf APC-3.1.8.tgz
cd APC-3.1.8
phpize
./configure --enable-apc --enable-apc-mmap --with-apxs --with-php-config=/usr/local/bin/php-config
make
make install
cd /usr/local/srcwget http://pecl.php.net/get/APC-3.1.9.tgztar -zxvf APC-3.1.9.tgzcd APC-3.1.9phpize./configure --enable-apc --enable-apc-mmap --with-apxs --with-php-config=/usr/local/bin/php-configmakemake install
Note: APC 3.1.9 was the latest stable release at the time this article was written, please check http://pecl.php.net/package/APC before proceeding to ensure you install the latest version.
Following your APC install, add the following lines to your global php.ini (/usr/local/lib/php.ini) to activate it:
extension="apc.so"apc.enabled=1apc.shm_segments=1apc.shm_size=128
Please remember that cPanel don't provide support for APC, but the benefit it can offer and the vast amount of information available on the internet about it can certainly make it worth it.