How to: drop back to the regular jenkins user - good practice
USER jenkins
```

In such a derived image, you can customize your jenkins instance with hook scripts or additional plugins.
For this purpose, use `/usr/share/jenkins/ref` as a place to define the default JENKINS_HOME content you
wish the target installation to look like :

```
FROM jenkins/jenkins:lts-jdk21
COPY --chown=jenkins:jenkins custom.groovy /usr/share/jenkins/ref/init.groovy.d/custom.groovy
```

If you need to maintain the entire init.groovy.d directory and have a persistent JENKINS_HOME you may run the docker image with `-e PRE_CLEAR_INIT_GROOVY_D=true`