Shallow Thoughts : : Jun

Akkana's Musings on Open Source Computing and Technology, Science, and Nature.

Sat, 03 Jun 2006

Cleaner, More Flexible Python Map Viewing

A few months ago, someone contacted me who was trying to use my PyTopo map display script for a different set of map data, the Topo! National Parks series. We exchanged some email about the format the maps used.

I'd been wanting to make PyTopo more general anyway, and already had some hacky code in my local version to let it use a local geologic map that I'd chopped into segments. So, faced with an Actual User (always a good incentive!), I took the opportunity to clean up the code, use some of Python's support for classes, and introduce several classes of map data.

I called it 0.5 beta 1 since it wasn't well tested. But in the last few days, I had occasion to do some map exploring, cleaned up a few remaining bugs, and implemented a feature which I hadn't gotten around to implementing in the new framework (saving maps to a file).

I think it's ready to use now. I'm going to do some more testing: after visiting the USGS Open House today and watching Jim Lienkaemper's narrated Virtual Tour of the Hayward Fault, I'm all fired up about trying again to find more online geologic map data. But meanwhile, PyTopo is feature complete and has the known bugs fixed. The latest version is on the PyTopo page.

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[ 18:25 Jun 03, 2006    More programming | permalink to this entry | comments ]

Thu, 01 Jun 2006

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!

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