Remote OS Detection using LPD Querying – Line printer daemons listening on TCP port 515 can give away information about which OS is running. Proof of concept code which contains a database of LPD returned messages and OS matches here.
You can download it from the following link: https://packetstormsecurity.com/files/download/24332/osdetect-lpd.txt
Source: https://packetstormsecurity.com/files/24332/osdetect-lpd.txt.html