1) Open the horde configuration file.

cd /usr/local/cpanel/base/horde/config
vi conf.php

2) Change the following two lines from:
$conf[’sql’][’hostspec’] = ‘localhost’;
$conf[’sessionhandler’][’params’][’hostspec’] = ‘localhost’;

To:

$conf[’sql’][’hostspec’] = ‘localhost:/var/lib/mysql/mysql.sock’;
$conf[’sessionhandler’][’params’][’hostspec’] = ‘localhost:/var/lib/mysql/mysql.sock’;