Error installing Rails on top of Ruby - ruby-on-rails

Question

When trying to run bundle install with MySQL I received:
An error occurred while installing json (1.8.3), and Bundler cannot continue.
Make sure that `gem install json -v '1.8.3'` succeeds before bundling.
I tried running:
sudo gem update
sudo gem update --system
sudo gem install rails
And got:
ERROR: Error installing rails:
activesupport requires Ruby version >= 2.2.2
Then I tried:
gpg --keyserver hkp://keys.gnupg.net --recv-keys 409B6B1796C275462A1703113804BB82D39DC0E3
\curl -sSL https://get.rvm.io | bash
\curl -sSL https://get.rvm.io | bash -s stable --ruby
\curl -sSL https://get.rvm.io | bash -s stable
And I got this:
pi#rpi:~ $ rvm use 2.3
Using /home/pi/.rvm/gems/ruby-2.3.0
pi#rpi:~ $ rvm use 2.3 --default
Using /home/pi/.rvm/gems/ruby-2.3.0
pi#rpi:~ $ sudo gem install rails
ERROR: Error installing rails:
activesupport requires Ruby version >= 2.2.2.
Why?

Answer 1

You used sudo with RVM. Don't do that if your RVM is installed in your user account, which yours appears to be.
When you use sudo you're running as the sysadmin, which doesn't know about Rubies in ~/.rvm, only the system-owned Ruby. That's why the version is wrong.
Search the RVM documentation on for "sudo" for more information. In particular this is important:
DO NOT use sudo...
to work with RVM gems. When you do sudo you are running commands as root, another user in another shell and hence all of the setup that RVM has done for you is ignored while the command runs under sudo (such things as GEM_HOME, etc...). So to reiterate, as soon as you 'sudo' you are running as the root system user which will clear out your environment as well as any files it creates are not able to be modified by your user and will result in strange things happening. (You will start to think that someone has a voodoo doll of your application...)
https://rvm.io/rubies/rubygems
In addition to the voodoo, you will have also installed and/or updated gems in the Ruby owned by the system, which can play havoc with other scripts which expect a certain behavior of a gem, which could have been changed by the update. That's an even worse situation because system tools or services can stop working, which will go unnoticed for a while.
So, don't use sudo with gem unless you're sure you know what you're doing.