If you install Jenkins natively on Ubuntu or Debian you may find that logging is not working. Logs should be saved to /var/log/jenkins/jenkins.log
Steps to get it working. Edit the service:
sudo vi /etc/systemd/system/multi-user.target.wants/jenkins.service
And uncomment this line (remove the #):
Environment="JENKINS_LOG=%L/jenkins/jenkins.log"
Then reload systemd:
sudo systemctl daemon-reload
Then restart Jenkins:
sudo service jenkins restart
Then you can view the logs:
tail -F /var/log/jenkins/jenkins.log