Biff is a mail notification system for UNIX.


When a new mail message is delivered, biff alerts the recipient so he can read it immediately. The alert is sent to the tty where the recipient is logged in, and contains the "Subject", "From" line, and first few lines of the body of the new message. The alert also includes terminal beeps to guarantee quick attention.

Notification is enabled by the command:biff yand disabled by:biff n


The MTA is responsible for starting the notification process. After delivering a message, it sends the recipient's username to the comsat daemon. The real work is then done by comsat, which finds out where the user is logged in and sends the alert there. Before sending an alert, it checks the user execute permission bit on the tty. This otherwise useless bit is set by biff y and cleared by biff n as an indication of the user's desire to receive mail notifications.


Because the sudden, unexpected printing of a block of text on a tty can be annoying if it overwrites more useful information on the screen that can't be easily regenerated, biff is not used very much any more. Some modern MTAs don't even support comsat, making biff useless.

The general idea of the incoming mail alert has remained very popular even as the original biff and comsat have been almost completely abandoned. There are many biff replacements, several with similar names like xbiff, xlbiff, kbiff, gnubiff, wmbiff, imapbiff and xbuffy. The concept also extends outside the UNIX world — the AOL "You've got mail" voice could be seen as a talking biff.


There was at least one vendor-specific version of biff that had a third mode of operation. In addition to y and n it could be set to b which would reduce the alert to just a pair of beeps, without any text written to the terminal. This made biff less disruptive. The feature has apparently died out.

Origin and name

biff came from 4.0BSD, and was named after a dog known by the developers at Berkeley, who – according to the UNIX man file – died on the 15th August 1993, at the age of 15, and belonged to a certain Heidi Stettner. Some sources [] [] report that the dog would bark at the mailman, making it a natural choice for the name of a mail notification system. The Jargon File contradicts [] this description, but confirms at least that the dog existed.

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