Installing Rails on Debian or Ubuntu is quite simple.

# aptitude update
# aptitude upgrade

to make sure you have everything up to date.

Then, run

# aptitude install rubygems build-essential

This will install gem, the ruby package manager, and pull in ruby if you don’t have it installed already. The build-essential package isn’t required for rails itself, but assuming you’ll ever want to install a gem with native extensions (like mongrel), you’ll need it.

Don’t forget to export the path via /etc/bash.bashrc (eg:
export PATH=$PATH:/var/lib/gems/1.8/bin)

Lastly, we’ll install rails itself:

# gem install rails --include-dependencies

You’re done.

Note:

Do not install rails using apt-get/aptitude! The debian repository includes a very old and broken version.