How to add the local repository on nain.oso.chalmers.se

1) For an Ubuntu LTS release, add the following two lines to 
   /etc/apt/sources.list: 

   deb http://nain.oso.chalmers.se/oso/ubuntu/ xxx contrib
   deb-src http://nain.oso.chalmers.se/oso/ubuntu/ xxx contrib

   Replace 'xxx' with 'lucid' if you are still running Ubuntu 10.04 (LTS).
   Replace 'xxx' with 'precise' if you are still running Ubuntu 12.04 (LTS).
   Replace 'xxx' with 'trusty' if you are running Ubuntu 14.04 (LTS).
   Replace 'xxx' with 'xenial' if you are running Ubuntu 16.04 (LTS).
   Replace 'xxx' with 'bionic' if you are already running Ubuntu 18.04 (LTS).

   *Note for xs*: if you are running anything else than these Ubuntu releases, e.g.
   a version of Mint or plain Debian, you'll need to check which libmotif and libpng 
   version is used by your system. Run 

   > apt-cache search --names-only libmotif

   If    libmotif3       is listed, use lucid 
   If    libmotif4       is listed, use version later than lucid

   > apt-cache search --names-only libpng  # only relevant if not lucid
   
   If    libpng12-0      is listed, use precise or trusty
   If    libpng16-16     is listed, use xenial or bionic

2) add the GPG key which has been used for signing the packages

   > wget -q -O - http://nain.oso.chalmers.se/oso/ubuntu/gpg.key | sudo apt-key add -

3) now update your package cache and install the application you want, e.g.:

   > sudo apt-get update
   > sudo apt-get install xs

   Obviously you can also handle this via the Synaptic Package Manager or
   even the Ubuntu Software Centre.