3. Restricting Users

Now that you're keeping the bad people out, and only letting the good people in, you may need to make sure that the good people behave themselves. This is most easily done by not letting them do anything except run pppd. This may or may not be necessary. I restrict users because the system that I maintain is dedicated to VPN, so users have no business doing anything else on it.

3.1. sudo or not sudo

There is this neat little program called sudo that allows the admin on a Unix system to grant certain users the ability to run certain programs as root. This is necessary in this case since pppd must be run as root. You'll need to use this method if you want to allow users shell access. Read up on how to setup and use sudo in the sudo man page. Using sudo is best on multi-use systems that typically host a small number of trusted users.

If you decide to not allow users to have shell access, then the best way to keep them from gaining it is to make their shell pppd. This is done in the /etc/passwd file. You can see /etc/passwd file that I did this for the last three users. The last field of the /etc/passwd file is the user's shell. You needn't do anything special to pppd in order to make it work. It gets executed as root when the user connects. This is certainly the simplest setup to be had, as well as the most secure, and ideal for large scale and corporate systems. I describe exactly what all needs to be done later in this document. You can Section 7, “Server: Set up user accounts” if you like.