However it's installation is a quite involved ritual, well, not anymore. Realizing that the entry where I discussed a debian package for IRAF was the most visited one, I am posting a much better solution: installation scripts, you can use this scripts for installing IRAF (and related packages like ds9) in ubuntu, and in Scientific Linux (this script should also work in Opensuse and Fedora). Just download them anywere and follow the instructions on screen. This scripts are only small modifications from the original one by amd77. Just make sure you have installed csh (it is in the universe repository in ubuntu and quite probably in the distribution media of Fedora and Opensuse) , you just need to run the comand: bash installiraf_* and enter your password in Ubuntu or the root password in other distro, so here are the scripts (links not working):
cl) from the same directory.
Since I posted this (quite a long ago) there have been all sort of changes in of libraries/packages included in modern distributions. Since there is no simple way to address this isssue (there are 6 versions of Ubuntu, 6 of Fedora and 5 of opensuse in the past 3 years, and that not counting that both come in 32 and 64 bit versions) I declare the scripts dead.
Nonetheless, an iso image which includes an useful installer is now being offered at: http://www.astro.uson.mx/favilac/downloads/ubuntu-iraf/iso/IRAF_Ubuntu.iso. Just keep in mind that it only works for 32 bit kernels (which are the majority of installed kernels, anyway).
The same autor also offers a (rather outdated) set of rpms at http://www.astro.uson.mx/favilac/downloads/IRAF/ . Find out which one is better suited for your distro and add it to your repos. I have not tried to install from these rpms so I can not comment on them.