I'm trying to connect to a database that I have just set up and configured.

I'm using PDO but is dosen't seem to work, I get this error message:

ERROR: SQLSTATE[HY000] [2003] Can't connect to MySQL server on 'xxxxxxxxx' (111)

Notice: Undefined variable: pdo in /var/www/html/xxxx/xxxx on line 21

I read in another thread that errors like these might be caused by the fact that PDO dosen't come installed with the standard mysql installation?

How can I install PDO? My version of PHP is PHP 5.5.9-1ubuntu4.14