linux-identd is a user identification daemon for Linux, which implements the Identification Protocol (RFC1413). This protocol is used to identify active TCP connections. The daemon listens to TCP port 113 (auth), and can be run either as a stand-alone daemon, or through inetd.
you may or may not have it installed, you could check by
if it's actually not installed then you can get it from the link above. just to add here there are many threads here concerning this, so, you should be able to find everything you need to get it up and running from here