To serve site locally

Using Ruby installer

Follow instructions here

After install:
sudo gem update

sudo gem install jekyll -v 3.8.5 Use current version on Github Pages
sudo gem install bundler

To serve to localhost

bundle exec jekyll serve

127.0.0.1:4000

Using Ubuntu or Windows Subsystem for Linux Ubuntu.

To install

sudo apt-get update -y && sudo apt-get upgrade -y

sudo apt-add-repository ppa:brightbox/ruby-ng

sudo apt-get update

sudo apt-get install ruby2.5 ruby2.5-dev build-essential dh-autoreconf zlib1g-dev

sudo gem update

sudo gem install jekyll -v 3.8.5 Use current version on Github Pages
sudo gem install bundler

To serve to localhost

bundle exec jekyll serve

127.0.0.1:4000