Install ruby:
$ sudo apt install ruby-full
Install build-essentials:
$ sudo apt install build-essential
Solution for 'Cant find gem bundler (>= 0.a) with executable bundle' https://bundler.io/blog/2019/05/14/solutions-for-cant-find-gem-bundler-with-executable-bundle.html:
$ sudo gem update --system
Install bundler and jekyll:
$ sudo gem install bundler jekyll
$ bundle update --bundler
Run:
jekyll serve