I have a Jenkins installation which runs as a Windows Service under a specific user. Now, we want to be able to access the UI for system tests, which is not allowed with this user.
My idea was to start Jenkins from the command line (using Jenkins.war) such that it is run with allowance of desktop interaction, while still using the specific user.
However, when I run this I get an 'empty' Jenkins, so nothing is configured (no settings, no jobs). Do I have to do something special to run Jenkins from the command line retaining the settings and jobs once it has been installed as a service?
Jenkins stores its configuration in a directory (called JENKINS_HOME), whose location is generally based on the user under which Jenkins is running.
You can see where this is via: Manage Jenkins > Configure System > Home directory (at the top of the page).
To run Jenkins as another user, you need to copy the JENKINS_HOME contents to the "Home directory" value you see when running that user (probably something like c:\users\username\.jenkins).
Or you can set the JENKINS_HOME environment variable to point to the system installation directory (if you installed from the MSI, this is likely within c:\Program Files (x86)\jenkins). Then Jenkins will start up, reading the existing settings and jobs. Though in this case, you need to make sure that your user has the same access rights as the system service had.