RVM, or Ruby Version Manager is a popular and effective way to manage running multiple Ruby environments. Here is how you set it up on CentOS 5.5:
1) Add the Webtatic respository and install Git.
rpm -Uvh http://repo.webtatic.com/yum/centos/5/latest.rpm yum install --enablerepo=webtatic git
(Note that this command will also install the perl-Error and perl-Git dependencies)
2) Create an rvm user and group.
groupadd rvm useradd -g rvm rvm
3) Add the root user to the rvm group (required for installation)
usermod -a -G rvm root
4) Install RVM as root.
bash < <(curl -L http://bit.ly/rvm-install-system-wide)
% Total % Received % Xferd Average Speed Time Time Time Current
Dload Upload Total Spent Left Speed
100 5840 100 5840 0 0 1620 0 0:00:03 0:00:03 --:--:-- 5653
Group 'rvm' exists, proceeding with installation.
Adding 'root' to the group 'rvm'
Creating the destination dir and making sure the permissions are correct
Cloning into rvm...
remote: Counting objects: 4206, done.
remote: Compressing objects: 100% (2029/2029), done.
Receiving objects: 26% (1094/4206), 796.00 KiB | 54 KiB/s
....
Setting up group permissions
Generating system wide rvmrc
Generating /usr/local/lib/rvm to load rvm
Correct permissions on rvmrc and the rvm loader
RVM is now installed. To use, source '/usr/local/lib/rvm' to your shell profile.
5) Install zlib via RVM.
# rvm package install zlib
Fetching zlib-1.2.5.tar.gz to /usr/local/rvm/archives
% Total % Received % Xferd Average Speed Time Time Time Current
Dload Upload Total Spent Left Speed
100 531k 100 531k 0 0 206k 0 0:00:02 0:00:02 --:--:-- 226k
Extracting zlib-1.2.5.tar.gz to /usr/local/rvm/src
Configuring zlib in /usr/local/rvm/src/zlib-1.2.5.
Compiling zlib in /usr/local/rvm/src/zlib-1.2.5.
Installing zlib to /usr/local/rvm/usr
6) Install Ruby 1.9.2 using RVM.
# rvm install 1.9.2 -C --with-zlib-dir=/usr/local/rvm/src/
Installing Ruby from source to: /usr/local/rvm/rubi
while depending on your cpu(s)...
ruby-1.9.2-p180 - #fetching
ruby-1.9.2-p180 - #extracting ruby-1.9.2-p180 to /u
ruby-1.9.2-p180 - #extracted to /usr/local/rvm/src/
ruby-1.9.2-p180 - #configuring
ruby-1.9.2-p180 - #compiling
ruby-1.9.2-p180 - #installing
ruby-1.9.2-p180 - Updating #rubygems to the latest.
Removing old Rubygems files...
Installing rubygems dedicated to ruby-1.9.2-p180...
Installing rubygems for /usr/local/rvm/rubies/ruby-1.9.2-p180/bin/ruby
Installation of rubygems completed successfully.
ruby-1.9.2-p180 - Updating #rubygems to the latest.
Removing old Rubygems files...
Installing rubygems dedicated to ruby-1.9.2-p180...
Installing rubygems for /usr/local/rvm/rubies/ruby-1.9.2-p180/bin/ruby
Installation of rubygems completed successfully.
ruby-1.9.2-p180 - adjusting #shebangs for (gem irb erb ri rdoc testrb rake).
ruby-1.9.2-p180 - #importing default gemsets (/usr/local/rvm/gemsets/)
Install of ruby-1.9.2-p180 - #complete
7) Set the RVM default to version 1.9.2
# rvm --default use 1.9.2 Using /usr/local/rvm/gems/ruby-1.9.2-p180
8) Verify that Ruby version 1.9.2 was installed successfully.
# ruby -v ruby 1.9.2p180 (2011-02-18 revision 30909) [x86_64-linux]
9) Add this environment variable to root’s .bash_profile file.
[[ -s "/usr/local/rvm/scripts/rvm" ]] && . "/usr/local/rvm/scripts/rvm"
10) Install rails.
# gem install rails Fetching: activesupport-3.0.5.gem (100%) Fetching: builder-2.1.2.gem (100%) Fetching: i18n-0.5.0.gem (100%) ... Installing RDoc documentation for railties-3.0.5... Installing RDoc documentation for bundler-1.0.10... Installing RDoc documentation for rails-3.0.5...< /pre>
UPDATE 7/25/2011: The system-wide install script is no longer available on github, and has been removed by the author. A workaround link is posted in the comments on this Stack Overflow discussion.