Deprecation of Ruby
I encountered this problem while taking over a very old Jenkins server (looks like it has not been properly maintained for >4 years). While booting up, I encountered the following problem
Loading plugin ruby-runtime v0.12 (ruby-runtime) failed perhaps due to plugin dependency issues
java.lang.RuntimeException: unsupported Java version: 11
However, it is impossible to boot up Jenkins with any earlier Java version, as Jenkins requires Java 11. Now we seem to end up in a dependency conflict.
This error happens because ruby-runtime has been deprecated for a long time (since 2018, see JEP 7). Thus, the remaining old plugins have prevented Jenkins from starting up.
The solution is to ssh into the server and manually disable the related plugins (for us,
ruby-runtime) by creating the files
Then, restart Jenkins. It should be good to run again.