RVM is a command-line tool which allows you to easily install, manage, and work with multiple ruby environments from interpreters to sets of gems. In this documentation I will show how to install RVM on CentOS 6.6.

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Install Development Tools

sudo yum groupinstall "Development Tools"

Install mpapis public key

sudo gpg2 --keyserver hkp://keys.gnupg.net --recv-keys 409B6B1796C275462A1703113804BB82D39DC0E3

or if failed

curl -sSL https://rvm.io/mpapis.asc | sudo gpg2 --import -

Install RVM for multiuser installation

\curl -sSL https://get.rvm.io | sudo bash -s stable

Add your user to rvm group

sudo usermod -aG rvm <user>

Logout and login again then install Ruby

rvm install 2.1
rvm use --default 2.1

You have installed Ruby version 2.1 and set it as your default version of Ruby.

ruby -v
ruby 2.1.5p273 (2014-11-13 revision 48405) [x86_64-linux]

Reference: https://rvm.io/rvm/install