Investigating TTYs and PTYs and writing to them
In this recipe, we'll learn how to list currently logged-in users, which TTYs they use, and which programs they are running. We'll also learn how to write to those users and terminals. As we'll see in this recipe, we can write to a terminal device just as if it were a file, assuming we have the correct permissions.
Knowing how to write to other terminals deepens understanding of how terminals work and what they are. It also enables you to write some interesting software and, above all, it will make you a better system administrator. It also teaches you about terminal security.
How to do it…
We'll start by investigating the logged-in users; then, we'll learn how to send messages to them:
- To make things a bit more interesting, open up three to four terminal windows. If you're not using the X-Window System, log in on multiple TTYs. Or, if you are using a remote server, log in several...
