slave.jar is meant to be launched by Jenkins, typically through a remote shell like ssh/rsh.
Jenkins master then communicates with this slave agent through stdin and stdout.
slave.jar is not meant to initiate a connection to the master on its own, so if you are trying to run
it from cron or as a service, you are misunderstanding how this works.
% java -jar slave.jar WARNING: Are you running slave agent from an interactive console? If so, you are probably using it incorrectly. See http://wiki.jenkins-ci.org/display/JENKINS/Launching+slave.jar+from+from+console