/var/run/utmp
to find out who's logged on and on what terminals
Biff server
comsat
Comsat is the server process which receives reports of incoming mail and notifies users if they have requested this service. Comsat receives messages on a datagram port associated with the “biff” service specification (see services(5) and inetd(8)). The one line messages are of the form:
user@mailbox-offset:/path/to/mailbox
If the user specified is logged in to the system and the associated terminal has the owner execute bit turned on (by a “biff y”), the offset is used as a seek offset into the appropriate mailbox file and the first 7 lines or 560 characters of the message are printed on the user's terminal. Lines which appear to be part of the message header other than the “From” or “Subject” lines are not included in the output.
/var/run/utmp
to find out who's logged on and on what terminals
18 releases since Debian 1.1 (Buzz); the text changed 3 times.