If you want to quickly find out the environmental variables available in your Hudson instance go to the following URL http://<your hudson instance>/env-vars.html
or this page also gives the list
Do you get this kind of error
“Hudson detected that you appear to be running more than one instance of Hudson that share the same home directory”
then its possibly because there are 2 instances of Hudson running.
I got this error when I deployed Hudson war in Tomcat server and set the ROOT context to point to the Hudson web application. Google search gave me this Hudson discussion link , which lead me to the solution.
I checked the running applications using Tomcat Manager web application, and found that 2 Hudson apps were installed one running at context /hudson and another at ROOT context. Solution to this problem was to remove the
<Context docBase=”hudson” path=””/>
entry from server.xml and then rename hudson directory under webapps to ROOT directory