Debugging Guide: Jenkins

Posted on March 18, 2025

Jenkins is an open-source automation server that enables developers to build, test, and deploy software applications more efficiently. It is a self-contained, Java-based program that can be deployed on-premises or in the cloud.

Common Use Cases:

  • Automating build and deployment processes for web applications
  • Integrating with version control systems like Git and SVN
  • Implementing continuous testing and feedback loops

Jenkins Logs via Jenkins Web Interface

Logs are available at this URL:

http://<your-jenkins-url:8080>/log

Jenkins Log Files

Linux (rpm and deb)

By default logs can be viewed by running:

journalctl -u jenkins.service

To customize the log location, run:

systemctl edit jenkins

and add the following:

[Service]
Environment="JENKINS_LOG=%L/jenkins/jenkins.log"

Windows (msi)

By default, logs should be at %JENKINS_HOME%/jenkins.out and %JENKINS_HOME%/jenkins.err, unless customized in %JENKINS_HOME%/jenkins.xml.

macOS

Log files should be at /var/log/jenkins/jenkins.log, unless customized in org.jenkins-ci.plist.

War file

When Jenkins is started from a command line with java -jar jenkins.war, the log file will be written to the JENKINS_HOME directory. If no value is assigned to the JENKINS_HOME environment variable, the log file will be written to the .jenkins/log directory.

Docker

If you run Jenkins inside Docker as a detached container, you can use the following command to view the Jenkins logs:

docker logs <containerId>

Some useful commands:

1) Check status of the service:

service jenkins status

OR

systemctl status jenkins

2) Restart the service:

service jenkins restart

OR

systemctl restart jenkins

3) Various ways to check journal entries

Show all journal entries:

journalctl -u jenkins --all

Show the last 100 lines:

journalctl -u jenkins -n 100

Show journal entries since last boot:

journalctl -u jenkins -b

Show journal entries for a specific time period:

journalctl -u jenkins --since=yesterday
journalctl -u jenkins --since=1hour ago

Check File System Permissions

Verify that the Jenkins user has the necessary permissions to read and write files in the Jenkins home directory.

On Linux:

sudo chown -R jenkins:jenkins /var/lib/jenkins

How to solve the error:
“Jenkins.service: start operation timed out. Terminating”

Try increasing the systemd timeout to give Jenkins more time to start:

sudo systemctl edit jenkins.service

Add the following lines:

[Service]
TimeoutStartSec=300

How to retrieve deleted Jenkins job

You should have this plugin installed beforehand: JobConfigHistory Plugin

Then go to this URL to reactivate your deleted Jenkins job: 

http://<your_jenkins_url>/jobConfigHistory/?filter=deleted

Useful links:

Leave a Reply