The commands to install rails on page 10 are missing some needed elements.
from page 10:
$ sudo apt-get install-y \
build-essential \
git \
libsqlite3-dev \
libyaml-dev \
ruby-bundler \
ruby-dev \
tzdata
Comparing with the Install Ruby on Rails Guide — Ruby on Rails Guides
sudo apt install build-essential rustc libssl-dev libyaml-dev zlib1g-dev libgmp-dev
The absence of libssl-dev and zlib1g-dev have caused me hours of confusion and troubleshooting. Today I finally figured out the omissions and figured they will cause others issues as well.