rlprd is a proxy which runs between the remote printing commands
(rlpr(1), rlpq(1), and rlprm(1)) and standard
lpd print servers in situations where the remote printing
commands cannot be installed setuid root. For a discussion on how to
configure the remote printing commands, please see rlpr(1).
rlprd needs to be installed setuid root - if it cannot be run this
way, it is useless.
rlprd works by mapping non-privileged port requests from
rlpr(1) clients to privileged ports so that lpds will
listen to them. Eliminating the "security" gained by having
privileged ports is a non-issue, since the Internet is no longer just
Unix, and Unix is the only OS that has the privileged port concept.
rlprd is not a replacement for lpd(8). It merely
passes data to a lpd(8) on a target machine (which is specified
by an invocation of a remote printing command). However, when
a client is using the rlpr suite of tools to do remote printing,
the client does not need to run an lpd(8) locally.
Note that once an rlprd is set up on a network (including the
Internet), any host may connect to it and use its proxy services if it
knows the name of the machine running it.