Debian installer no longer supports Ubuntu 18.04 or Debian 9

[MarkEWaite]

Describe your use-case which is not covered by existing documentation.

https://github.com/jenkinsci/packaging/issues/455 reports that the Debian installer did not include all the necessary components to easily support Unix domain socket communication with the Jenkins controller. https://github.com/jenkinsci/packaging/pull/456 fixes that issue beginning in Jenkins 2.451 to allow easier use of Unix domain sockets with the Debian installer.

The Jenkins 2.451 fix in https://github.com/jenkinsci/packaging/pull/456 updates the Debian installer to require Debian 10 as the minimum supported Debian version and to require Ubuntu 20.04 as the minimum supported Ubuntu version. Debian 9 and earlier are not supported by the Jenkins project. Ubuntu 18.04 and earlier are not supported by the Jenkins project.

The packaging improvement in https://github.com/jenkinsci/packaging/pull/456 prevents the Debian package from installing on Debian 9 or on Ubuntu 18.04. Prior to Jenkins 2.451, Debian 9 and Ubuntu 18.04 were unsupported but were expected to work with Jenkins. Beginning with Jenkins 2.451, Debian 9 and Ubuntu 18.04 cannot use the Jenkins debian package.

The next LTS baseline is expected to include this change in the release that is planned for 15 May 2024.

Reference any relevant documentation, other materials or issues/pull requests that can be used for inspiration.

If a user attempts to install Jenkins 2.451 or later on Ubuntu 18.04 or Debian 9, the apt package manager will refuse to install it with the message:

pre-depends on init-system-helpers (>= 1.54)

Users that must continue running Jenkins on those unsupported operating systems may switch from installing with the Debian package to install the war file and create the service themselves.