<services>
    <emulab:program-agent name="prog0"
         command="/bin/ls -lt &gt;&amp; /tmp/foo"
         onexpstart="true"/>
  </services>

Much like a normal "execute" service, these are event agents instead
of boot commands (which run on every boot of the node). When onexpstart
is true, the command is run at event time=0 only. All program agents
are set up to respond to tevc commands like program agents in an classic
Emulab experiment.