Something’s changed since last time I played around with Ubuntu, some packages such as irb and rdoc live in the universal repository and, by default, this is disabled so when you go to install it it’ll say it’s not found:
sudo apt-get install rdoc Reading package lists... Done Building dependency tree Reading state information... Done Package rdoc is not available, but is referred to by another package. This may mean that the package is missing, has been obsoleted, or is only available from another source E: Package rdoc has no installation candidate
Uncomment the following lines using sudo vim /etc/apt/sources.list:
#deb http://us.archive.ubuntu.com/ubuntu/ jaunty universe #deb-src http://us.archive.ubuntu.com/ubuntu/ jaunty universe #deb http://us.archive.ubuntu.com/ubuntu/ jaunty-updates universe #deb-src http://us.archive.ubuntu.com/ubuntu/ jaunty-updates universe
And then run sudo apt-get update and you should be able to install irb and rdoc now.
rdoc is required for installing rubygems, and that’s where I got hung up for a couple of minutes before I found the docs on ruby-lang.org under Ruby on Linux.