Summary:
Setting up Jenkins on OS X has been made significantly easier with the most recent installer (as of 1.449 - March 9, 2012), however managing the pr
To change the password you can use sudo passwd jenkins . However I think it would be better to use the dscl command to change the password.
In my install jenkins (official installer) had a user shell /usr/bin/false. Changing it to bash solved the problem of not being able to login:
sudo dscl . -change /Users/jenkins UserShell /usr/bin/false /bin/bash
You should now be able to login with su jenkins.