Some time ago, a PPC/Mac OS X 10.5 build slave used with Jenkins started consistently failing with a java.io.IOException: Unexpected termination of the channel due error on some Jenkins slaves.

Relaunching the agent showed the reason for the error was due to a java.lang.InternalError: Can't connect to window server exception.

This was fixed, based on some insight from StackOverflow, by setting -Djava.awt.headless=true in the Advanced/JVM Options for this host.