On Debian you can install it like this:
apt-get install php5-xmlrpc
XML-RPC support in PHP is not enabled by default. You will need to use the --with-xmlrpc[=DIR] configuration option when compiling PHP to enable XML-RPC support. This extension is bundled into PHP as of 4.1.0.
The easiest way to install XML-RPC in CentOS (migth not work on CentOS 7):
yum install php-xmlrpc
service httpd restart
Ready to go!
Note: On OSX uncomment the following line in php.ini :
Note: On Windows you just have to uncomment the following line in php.ini :-