From the
identd(1)
manpage in
Debian:
Identd is a server which implements the TCP/IP proposed
standard IDENT user identification protocol as specified
in the RFC 1413 document.
identd operates by looking up specific TCP/IP connections
and returning the user name of the process owning the connection. It can optionally return other information
instead of a user name.
In other words, if you have many
users on your
computer and one of them initiates a
network socket to a
remote host,
identd lets the remote host know which user on your system did so. This permits the remote host's
sysadmin to
report or
ban people by
username@
host rather than banning your whole
host if one of your
users does something
stupid -- and, in other ways (as
MrFurious points out below) take actions on the basis of
username.
Why is identd important to you on a private workstation? Well, for the above reasons, many IRC servers and some FTP servers will refuse to accept a connection from you unless they can get user identification from identd on your system.
Notes: