title: Jenkins - cannot log in after a fresh install
body: <p>Installed Jenkins 2.39 on Debian as per <a href="http://pkg.jenkins-ci.org/debian/" rel="nofollow noreferrer">http://pkg.jenkins-ci.org/debian/</a>. Opened it in browser (Firefox) and it's asking for credentials from the log file; copied and pasted that password but it doesn't work. Disabled useSecurity (and friends) in /var/lib/jenkins/config.xml, restarted Jenkins but to no avail: it still asks for password <em>and</em> it overwrites all changes to config.xml. The config.xml is clobbered even when chown'd to root and set to read-only (444) access.
  Any ideas how to get out of that hole?</p>
  
  <p>UPDATE: apparently an obscure file has to be created in JENKINS_HOME directory with the contents 2 as described at <a href="https://stackoverflow.com/questions/35960883/how-to-unlock-jenkins">this link</a>. User friendliness at its peak.</p>