How to prevent users from installing non-free software?

Question

Is it possible to disable installation of non-free or proprietary softwares and applications in Ubuntu?

Answer 1

Tell them don't install non-free softwares. If this doesn't work, try:

1. Create user group powerusers, users in this group can only install certain type of softwres.

   # addgroup powerusers
   

2. Edit /etc/sudoers, grant powerusers the privilege to sudo apt-get only:

   %powerusers ALL = (ALL) /usr/bin/apt-get
   

   Now, users in powerusers group can only sudo apt-get ..., but can not sudo dpkg -i <downloaded.deb>, or edit file /etc/apt/sources.list. Only you can determine which sources to include.

3. Remove non-free, restricted, multiverse sources from sources.list files.

Done!

Answer 2

It is technically impossible!

Since the IQ level of a computer is zero, it can't detect whether the software running on it is free software or not. The only one thing you can do is advise users to use free software only. :-)