Note that if the port was not specified with the <installations><installation><agent_options><scheduler_http_port> element that would cause the global value 4445 to be applied to all Agent installations. In this example, this element is superfluous for the second installation.
The commands defined under <command> (in the section <installations><installation><postprocessing><command>) will be executed for each installations individually. In this example you would install the Agents on different UNIX distributions, the first one would be installed on an Ubuntu distribution (therefore commands like update-rc.d) and the second one would be installed on a CentOS distribution (therefore commands like chkconfig).