On slave status page, Jnlp launch options and control button are not available for VirtualBox slave. Options are available for non-VirtualBox slave:
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Slave Non-Vbox
Connect slave to Hudson one of these ways:

##"launch agent" button# Launch agent from browser on slave
*

Run from slave command line:

javaws http://hudson:8080/hudson/computer/Non-Vbox/slave-agent.jnlp

*

Or if the slave is headless:

java -jar slave.jar -jnlpUrl http://hudson:8080/hudson/computer/Non-Vbox/slave-agent.jnlp
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Options are not available for Virtualbox slave:
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Slave Vbox-slave

This node is offline because Hudson failed to launch the slave agent on it. See log for more details
##"Launch slave agent" button##
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Please make these jnlp options available on virtualbox slaves.