Do 'finger' and 'pinky' always show all users currently logged in?

Question

I've been playing around on my university's system and I noticed that sometimes the lists of logged in users I get from finger and pinky appear incomplete. For one thing, there were times when a friend sitting right next to me was logged in but I couldn't find them on the list. I checked to make sure and they were on the same exact computer (remote#) as me. Then there is the results of top. Sometimes it shows programs being run by users, but those users are nowhere to be found on the pinky list. Is there some exception where users can be logged in but not show up in pinky?

Answer 1

So there are several commands that can answer "who is using the system" with different meanings.

If you mean interactively using the system, the commands finger, pinky, w and who will list interactive logins. But there are several ways that will allow a user to not advertise their session, although it is not always possible to hide.

However, it is also possible to use the system in a non-interactive session, or leave background jobs on the system. A background job doesn't necessarily require the user to stay logged in. Commands like top and ps will list what users are running, interactive or not. There may be a column in the output of these programs called "tty" that will be blank for processes that are not part of an interactive session.

Finally, the last command (I recommend something like last -20 or last | less for busy systems) will show you who recently used the system and if they are still logged in.

And for extra fun, some systems may have enabled commands like talk and write which are precursors to today's instant messaging.