Jenkins, an open-source automation server, plays a crucial role in continuous integration and continuous delivery (CI/CD) processes. Updates are essential to keep Jenkins running smoothly and to benefit from the latest features, bug fixes, and security patches. In this blog post, we will explore the process of upgrading Jenkins from version 2.319.3 to 2.401.1.

Major changes in the new upgrade

Beginning with Jenkins 2.335 and Jenkins 2.332.1, the Jenkins project is migrating from System V init(8) to systemd(1) in its official Debian, Red Hat, and openSUSE packages.

Beginning in 2008, the Jenkins (then Hudson) project has delivered Linux OS installation packages for Debian (and derivatives), Red Hat (and derivatives), and openSUSE. These packages were all based on the System V init(8) system in common use at that time. A remnant of the venerable Unix System V from 1983, init(8) had remained unchanged for decades.

systemd(1) provides compatibility with the behavior exposed by System V init(8), and the System V init(8) scripts delivered in the Jenkins project’s official Linux OS packages continued to work in this compatibility mode. Beginning with Jenkins 2.335 and Jenkins 2.332.1, the Jenkins project’s official Linux OS packages deliver a native systemd(1)service unit, which supersedes the older System V init(8) scripts.

Package configuration

Users who run Jenkins 2.335 or later and 2.332.1 LTS or later through the official Debian, Red Hat, or openSUSE packages are affected by this migration.

The System V init(8) packages delivered the following configuration files:

Debian

/etc/default/jenkins

Red Hat

/etc/sysconfig/jenkins

openSUSE

/etc/sysconfig/jenkins

Each configuration file used a unique format, with the Debian version being radically different from the Red Hat and openSUSE versions. Furthermore, manual edits to these files would frequently conflict with updated upstream versions, triggering the package manager to flag the conflict and requiring manual intervention on upgrade.

When installed on a modern Linux distribution running systemd(1), the systemd(1) service unit is delivered to:

Debian

/lib/systemd/system/jenkins.service

Red Hat

/usr/lib/systemd/system/jenkins.service

openSUSE

/usr/lib/systemd/system/jenkins.service

The System V init(8) logic was asynchronous; i.e., running /etc/init.d/jenkins start would return prior to the completion of Jenkins startup. The systemd(1) logic is synchronous; i.e., running systemctl start jenkins will block until Jenkins signals successful startup. This allows system administrators to write automation to programmatically deploy Jenkins using modern tools like Ansible.

The systemd(1) package also uses systemd-journald(8) for logging by default. Rather than creating a log file in /var/log/jenkins/jenkins.log, Jenkins now logs to the system’s journal. Log entries may be viewed with journalctl -u jenkins.

Post upgrade tasks

• After the upgrade, log in to Jenkins UI and verify that you see the new version number at the bottom right corner.
• Navigate to ‘Manage Jenkins’ via the menu and Action any notifications displayed — plugins, about Jenkins, data format conversions, etc.