When starting Jenkins from a war archive, on a network behind a proxy.

The initial setup takes ages until Jenkins give up and ask for the initial admin password. Then the install page that selects the initial plugins never load. It is not possible to setup the proxy during initial startup in the UI.

Jenkins is started with the following command line

JENKINS_HOME=/jenkins-folder/ java -Dhttp.proxyHost=proxy.com -Dhttp.proxyPort=8080 -jar jenkins.war --httpPort=9090

Workaround is to copy the proxy.xml file from another working instance, then restart jenkins.