If after doing yum install you get the error: no package ... is available while you’re absolutely sure that the package you want to install is available in connected repositories, chances are that it is excluded in /etc/yum.conf.
My error was no package ftp is available. This happened because DirectAdmin excluded everything *ftp* presumably to avoid conflicts with the FTP daemon it takes care of, and ftp, the standard unix FTP client, hadn’t been initially installed on the server.