cups-lpd Linux Service

cups-lpd service:

CUPS Line Printer Daemon(LPD). It is a mini-server that supports legacy client systems that use the LPD protocol. It enables older Linux and commercial Unix systems to connect to cups server.
It is used to allow older systems access to the printers.

Now lets see the manual of cups-lpd service.
Manual cups-lpd:
NAME
cups-lpd - receive print jobs and report printer status to lpd clients
SYNOPSIS
cups-lpd [ -o option=value ]
DESCRIPTION
cups-lpd is the CUPS Line Printer Daemon ('LPD') mini-server that supports legacy client systems that use the LPD protocol. cups-lpd does not act as a standalone network daemon but instead operates using the Internet 'super-server' inetd(8). Add the following line to the inetd.conf file to enable the cups-lpd daemon:
printer stream tcp nowait lp /usr/lib/cups/daemon/cups-lpd cups-lpd
If you are using the newer xinetd(8) daemon, add the following lines to the xinetd.conf file:
service printer
{
socket_type = stream
protocol = tcp
wait = no
user = lp
server = /usr/lib/cups/daemon/cups-lpd
}
SECURITY
cups-lpd currently does not perform any access control based on the settings in cupsd.conf(5) or in the hosts.allow(5) or hosts.deny files used by TCP wrappers. Therefore, running cups-lpd on your server will allow any computer on your network (and perhaps the entire Internet) to print to your server.
While xinetd has built-in access control support, you should use the TCP wrappers package with inetd to limit access to only those computers that should be able to print through your server.
OPTIONS
The -o option to cups-lpd inserts options for all print queues. Most often this is used to disable the 'l' filter so that remote print jobs are filtered as needed for printing:
printer stream tcp nowait lp /usr/lib/cups/daemon/cups-lpd cups-lpd -o document-format=application/octet-stream
server = /usr/lib/cups/daemon/cups-lpd
server_args = -o document-format=application/octet-stream
The example shown resets the document format to be application/octet-stream, which forces auto-detection of the print file type.
COMPATIBILITY
cups-lpd does not enforce the restricted source port number specified in RFC 1179, as using restricted ports does not prevent determined users from submitting print jobs. While this behavior is different than standard Berkeley LPD implementations, it should not affect normal client operations.
The output of the status requests follows RFC 2569, Mapping between LPD and IPP Protocols. Since many LPD implementations stray from this definition, remote status reporting to LPD clients may be unreliable.
SEE ALSO
inetd(8), xinetd(8), CUPS Software Administrators Manual, http://localhost:631/documentation.html