IPP

Internet Printing Protocol which is what CUPS uses. You may know that if you fire up your web browser and point it at https://localhost:631 you get the CUPS administration screen, but did you realize that CUPS itself sends print and status requests to the same port?

There's nothing secret about this: CUPS documentation (which you can find at https://localhost:631/ipp.html ) explains all of it. If you wanted to, you could control CUPS directly with HTTP requests. We can demonstrate that with a little tom-foolery: let's create a little shell script that we'll run on port 631. First the script, which logs attempted connections.

#!/bin/bash
echo "Connection" >> /tmp/fakecupsd
date >> /tmp/fakecupsd
read line
echo $line >> /tmp/fakecupsd
 

We turn that on by creating a file in /etc/xinetd, stopping the real cups, and telling xinetd to start using ours for port 631 connections.

# cat /etc/xinetd.d/fakecups
service ipp
{
        socket_type     = stream
        wait            = no
        user            = root
        server          = /root/fakecups
}
/etc/init.d/cups stop
kill -1 `cat /var/run/xinetd.pid`
 

Now do an "lpstat -v" - it will hang, so ctrl-c it, and look in /tmp/fakecupsd. You'll see something like this repeated multiple times:

Connection
Sat Mar 26 05:36:30 EST 2005
POST / HTTP/1.1
 

The reason lpstat hangs is that it is sending more data with that http post, which the real cups daemon would process and acknowledge.

Got something to add? Send me email.

1 comment

Have you tried Searching this site?

This is a Unix/Linux resource website. It contains technical articles about Unix, Linux and general computing related subjects, opinion, news, help files, how-to's, tutorials and more.

Contact us