How to reset Jenkins security settings from the command line?

The simplest solution is to completely disable security - change true to false in /var/lib/jenkins/config.xml file.

<useSecurity>true</useSecurity>

A one-liner to achieve the same:

sed -i 's/<useSecurity>true<\/useSecurity>/<useSecurity>false<\/useSecurity>/g' /var/lib/jenkins/config.xml

Then just restart Jenkins:

sudo service jenkins restart

And then go to admin panel and set everything once again.

If you in case are running your Jenkins inside a Kubernetes pod and can not run service command, then you can just restart Jenkins by deleting the pod:

kubectl delete pod <jenkins-pod-name>

Once the command was issued, Kubernetes will terminate the old pod and start a new one.

One other way would be to manually edit the configuration file for your user (e.g. /var/lib/jenkins/users/username/config.xml) and update the contents of passwordHash:

<passwordHash>#jbcrypt:$2a$10$razd3L1aXndFfBNHO95aj.IVrFydsxkcQCcLmujmFQzll3hcUrY7S</passwordHash>

Once you have done this, just restart Jenkins and log in using this password:

test

I found the file in question located in /var/lib/jenkins called config.xml, modifying that fixed the issue.