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Internet Printing Protocol which is what CUPS uses. You may know that if you fire up your web browser and point it at http://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 http://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.

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:

Sat Mar 26 05:36:30 EST 2005

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

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© Tony Lawrence

Thu Mar 31 13:46:18 2005: 264   drag

I prefer using IPP over using something like SAMBA. It seems much nicer to me.

Windows clients support IPP since Windows 2000, and I've tried it and it works very well... for me. IPP basicly turns your computer in a postscript-compatable networked printer.

But I've been told that Windows IPP support is sub-par and usually SAMBA is going to be better for large numbers of windows clients.

Although if you use Unix ones, especially ones that use CUPS (ie: Linux or FreeBSD or OS 10.2(10.2.4(?)) or newer) then it rocks.


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