OLPC Library – Trying to get XOs out of people wardrobes

XOs at LCA08

This time last year was a very exciting time at linux.conf.au 2008. The conference organisers had arranged for 100 XO laptops to be given away to conference attendees.

The XOs came with the following message attached.

Please do something wonderful with this XO, or inspire someone else and pass it on.

I was fortunate enough to get one of these XOs. I knew however that I wouldn’t have any time in the foreseeable future to actually do anything cool with my XO. At the same time I didn’t simply want to give it away to someone, since I knew at some stage I would actually want to do something with it.

After chatting this over with a few other people I came up with the idea of putting together an OLPC Library. (It was originally going to be OLPC Bank but after chatting it over with Pia we decided that a Library seemed to fit the ideals of the project much better).

So as part of the work I’m doing with OLPC Friends we have finally launched OLPC Library. At the moment this is just a place holder page but hopefully soon we will have a site up to actually enable people to loan out OLPCs whether that be to a developer wanting to write a new piece of software/port an application or a community advocate putting on a demo at a school or trade show.

If you are interested in helping out you can see the beginnings of the ideas for the website at the OLPC Library Project page and you can also join the mailing lists.

OLPC Wireless packet loss

Last week Pia asked me to help her out with her yet to be name Australian OLPC deployment. The deployment involves two remote sites connected by an ADSL WAN and one of the key applications across this LAN is the use of the VideoChat activity.

The children at the site were experiencing audio blips and video artefacts, a sure sign of some sort of network related packet loss. With Pia at one site and myself at the other we did some testing to try and rule out the WAN itself as the problem and determine what the issue was.

It became quickly obvious that the WAN wasn’t at fault. We setup some pings with an interval of 1/10 of a second from the XO’s to their respective default gateways and between the default gateways themselves. Pia and I then started counting out loud, which got us a couple of strange looks from children playing around us :). During the audio blips there was no loss across the WAN but there was loss to the default gateways.

Now here comes the interesting part, the packet loss to the default gateways seemed to be syncronised. Now remember these are totally independant wireless networks sitting a couple of 100 kilometers apart. At this stage I was cooking up crazy theories about difficult to decode/encode video packets hitting both XOs at the same time but I was fairly dubious.

We did a little testing on XOs at the same site and while the problem didn’t seem to manifest in as obvious a manner it was still there (I think the latency involved across the WAN exacerbated the symptoms).

Back at home I did some further testing for a few days, trying all manner of different loads and writing various script to watch tcpdump output. To cut a long story short eventually while glancing at the XO during packet loss I noticed the antennae light was flashing which would indicate the XO is disassociating from the network.

A few minutes later I was able to verify that wireless scans were causing the problem and that it is easily reproducible by doing

ping -i 0.1 GATEWAY_IP &

iwlist eth0 scan

You should notice the drop of about 4 packets.

I’ve filed the bug on the OLPC bug tracker

Ticket #9048 – Wireless scanning causes network pauses

A temporary work around is to get Network Manager to stop performing scans, although I assume this means the network view probably won’t get updated. You can do this using wpa_cli.

> ap_scan 0

Getting your key into debian-maintainers using jetring

I’m currently going through the process of becoming a Debian Maintainer so that I can upload Annodex packages without bugging one of the DDs I know. Thanks to horms and jaq for their help thus far.

As part of this process you need to file a bug against the debian-maintainers package to get your key added. You need to do this using a piece of software called jetring. jetring allows you to create changesets for a gpg keyring, a binary format, to make it easy for the maintainers to add and remove keys and know exactly whats being added and removed. I couldn’t find very much information on how you actually do this and hence the reason for this post.

To start with you need to grab the latest copy of the debian-maintainers keyring and extract the actual keyring from it. You can find the link to the latest version at debian-maintainers, just click on all to download it.

Here is the process I followed with comments along the way

# Download the latest debian-maintainers keyring
wget http://http.us.debian.org/debian/pool/main/d/
dpkg-deb -x *.deb keyring
mv keyring/usr/share/keyrings/debian-maintainers.gpg .
rm -rf keyring *.deb

# Create a copy of it and add your key to it
cp debian-maintainers.gpg debian-maintainers.gpg.orig
gpg --export johnf@inodes.org | 
    gpg --import --no-default-keyring --keyring `pwd`/debian-maintainers.gpg

# Create the changset with jetring
jetring-gen debian-maintainers.gpg.orig debian-maintainers.gpg 
    "Add John Ferlito <johnf @inodes.org> as a Debian Maintainer"

# Check the changeset
jetring-review -d debian-maintainers.gpg.orig add-*

Once you have completed the above you should have a file with something like the following contents

Comment: Add John Ferlito <johnf @inodes.org> as a Debian Maintainer
Date: Sat, 05 Jul 2008 14:26:31 +1000
Action: import
  Version: GnuPG v1.4.6 (GNU/Linux)

You should now add something along the lines of the below to the top of the file.

  Simon Horman <horms @verge,net.au>,
  Jamie Wilkinson <jaq @spacepants.org>
Agreement: http://lists.debian.org/debian-newmaint/2008/07/msg00010.html

The agreement line should be a URL to your signed email applying to become a DM and the advocates should be the URLs for the signed emails from your advocates.

Once you’ve done that, submit a bug with the file attached and hopefully sometime later you will have become a DM.

Sorting in Mutt

A couple of days ago I discovered the following mutt config option.

set sort = threads
set sort_aux = last-date-received

This means you get the usual threading but that a thread is sorted by the date the last message in the thread was received. This keeps a thread which receives new mail at the bottom of your mailbox rather than up at the top.

Another idea I found useful is to sort my spam mailbox by subject. Since a lot of SPAM has exactly the same subject it makes it really easily to quickly scan the mailbox for HAM.

You can easily do this with the following additions to your muttrc

folder-hook . set sort=threads
folder-hook spam set sort=subject

You need to set the default as mutt will change the sort order when you change to the spam folder but won’t change it back when you jump out of it.

EC2UI extension for Firefox 3

I’ve been doing some work with Amazon EC2 the last few days. An invaluable tool is the EC2UI firefox extension that Amazon have written. This provides you with a simple GUI inside the firefox chrome which makes it really easy to manipulate your EC2 instances.

A few weeks ago Hardy moved to using firefox 3. This meant, amongst other things, that the amazon plugin stopped working. The firefox guys have a webpage up that explains how to update extensions for Firefox 3.

The main problem was with changes to the password manager. You can find my changes on my bzr branch and a packaged up version of the extension EC2UI for Firefox 3.0b4.

Update: See comments below for new versions