I may be missing something (I didn't see any references to this in recent issues or discussions), but when I try to uninstall eXist 3.0 on an Ubuntu 14.04 server, I get an error:
"Error: Invalid or corrupt jarfile uninstall.jar"
(this after changing the file permissions to executable).
Also, I may have goofed during the command-prompt install, but I seem to have had an issue with my admin password: is there a restriction on passwords with spaces? When I tried to log in to the dashboard, the password I used during install wouldn't work (it did contain space characters). That's when I tried to uninstall and had the issue with the JAR file.
-- Tim A. Thompson Metadata Librarian (Spanish/Portuguese Specialty) Princeton University Library