PHP5.6 and APC installation

APC is (more or less) a deprecated package (the last release, 3.1.14, was unstable and had to be rolled back). It has been replaced by the core package opcache.

I'm not sure about Debian flavors (all my searches return the PECL library while opcache is native to 5.6) but in CentOS you have to install the php-opcache package, which contains the opcahce.so file.

It works for me

yum install php56w-pecl-apcu

For Amazon Linux, The below command worked for me.

yum install php56-pecl-apcu