The Secret to the CUPS Web Interface (Shallow Thoughts)

The Secret to the CUPS Web Interface

On Dapper, whenever I tried to add a new printer or make any modifications to the existing printer's settings, I would eventually come to a dialog prompting me to enter username and password for 'CUPS'. There seemed to be no right answer: there is no user called "cups" (there's a "cupsys", but that's not what it was asking for), and trying either my own username and password, or root's, just popped up the dialog again. A second attempt always led to a blank white page.

But Carla knew the answer. You're supposed to read:

zless /usr/share/doc/cupsys/README.Debian.gz

then skip to the end of the file where there's a brief hint about this problem, stating that "Administration over the web interface is disabled by default since it requires the CUPS daemon to be able to read /etc/shadow." Note that they don't actually disable it in a way that tells users it's disabled. CUPS apparently doesn't check for read permission on the shadow file before opening it, or check whether there was an error in reading it; it just silently bombs out with no indication what went wrong.

To fix it:

adduser cupsys shadow
adduser yourname lpadmin

You may not need the second line if you're already in group lpadmin (type groups to find out).

Then reboot. (Restarting cups and logging out and back in might be enough: you need to get cups and your login session seeing their new group permissions.)

Now, magically, the CUPS web interface works!

Tags: linux, printing
[ 23:15 Jun 01, 2006    More linux | permalink to this entry | ]