README

sshlpr2

INTRODUCTION

When your printer is connected to your SSH server, but not to you, you can
use sshlpr2 to create a CUPS printer that behaves like a remote server.

Similar work was done by Andre Masella. His original sshlpr script can be
found at

http://www.masella.name/technical/sshlpr.html

The original version of sshlpr has two problems:

(1) Requires your SSH server to accept public key authentication. Password
authentication will certainly fail, because when ssh is run by CUPS it
is not able to open a terminal.

(2) Requires CUPS to run su, which will also fail because CUPS is not
connected to a terminal.

To avoid the su problems, sshlpr2 has a simple server daemon that accepts
jobs submitted to it (via the sshlpr backend) and forwards the jobs to
clients attached to it (via sshlpr_client).

sshlpr_client can be run in an X environment, so that you can launch xterm
and key in your password. sshlpr_client is setuid lp, in order to allow you
to connect to sshlprd.

INSTALLATION

On a regular Ubuntu system, type:

$ ./configure; make; sudo make install

If you are on other Linux/Mac system, have a look at the configure options
specific to sshlpr2:

  --with-cups-backend     CUPS backend directory, e.g. /usr/lib/cups/backend
  --with-socket-dir       Socket directory, e.g. /var/sshlpr
  --with-lpuser           Username to setuid the CUPS backend and client

HOW IT WORKS

0. Initialization
	a) sshlprd is running.
	b) Some user runs sshlpr_client, which connects to sshlprd

1. sshlpr
	a) Creates a FIFO in /tmp
	b) Submits job request to sshlprd

2. sshlpr_client
	a) Receives the job request from sshlprd
	b) Executes sshlpr_helper, passing parameters from the job request
		to sshlpr_helper

3. sshlpr_helper
	a) Reads the parameters
	b) Starts an xterm process that:
		i]   Reads from the FIFO, and pipes the output to...
		ii]  ... an ssh process that runs the ...
		iii] ... lpr process on the remote end

HOW TO USE IT

After installation, create a printer based on the sshlpr2 backend on

sshlpr://abc123@linux.pwf.cam.ac.uk/Pem_CC_1_BW

Unlike the original sshlpr, the local user does not have to be specified,
because you will always execute ssh as the user that created the print job.

SPECIAL NOTE TO UNIVERSITY OF CAMBRIDGE USERS

To discover your list of printers:

	ssh <CRSID>@linux.pwf.cam.ac.uk 'lpstat -P -a'