As root:

cd src/rubygems-1.3.7
export RUBYOPT=""
ruby setup.rb

RUBYOPT is set in .bashrc to include ruby gems, but means that ruby will fail if it can't find a working gems install.

Gems commonly used:

• mini_exiftool (which requires command-line tool exiftool, source package Image-ExifTool-X.XX.tar.gz)
• exifr (now rarely used in favour of mini_exiftool, which has read-write access)
• fileutils

su  # gems can be installed for one user only but otherwise need to be run as administrator or root
gem update --system
gem install mini_exiftool

• Qt4 (libraries and SDK, currently 400+MB): http://qt.nokia.com/downloads
• qt4-qtruby: http://rubyforge.org/projects/korundum/

• exiftool
• jhead
• gems listed above