Petter Reinholdtsen

Entries from October 2013.

Teaching vmdebootstrap to create Raspberry Pi SD card images
27th October 2013

The vmdebootstrap program is a a very nice system to create virtual machine images. It create a image file, add a partition table, mount it and run debootstrap in the mounted directory to create a Debian system on a stick. Yesterday, I decided to try to teach it how to make images for Raspberry Pi, as part of a plan to simplify the build system for the FreedomBox project. The FreedomBox project already uses vmdebootstrap for the virtualbox images, but its current build system made multistrap based system for Dreamplug images, and it is lacking support for Raspberry Pi.

Armed with the knowledge on how to build "foreign" (aka non-native architecture) chroots for Raspberry Pi, I dived into the vmdebootstrap code and adjusted it to be able to build armel images on my amd64 Debian laptop. I ended up giving vmdebootstrap five new options, allowing me to replicate the image creation process I use to make Debian Jessie based mesh node images for the Raspberry Pi. First, the --foreign /path/to/binfm_handler option tell vmdebootstrap to call debootstrap with --foreign and to copy the handler into the generated chroot before running the second stage. This allow vmdebootstrap to create armel images on an amd64 host. Next I added two new options --bootsize size and --boottype fstype to teach it to create a separate /boot/ partition with the given file system type, allowing me to create an image with a vfat partition for the /boot/ stuff. I also added a --variant variant option to allow me to create smaller images without the Debian base system packages installed. Finally, I added an option --no-extlinux to tell vmdebootstrap to not install extlinux as a boot loader. It is not needed on the Raspberry Pi and probably most other non-x86 architectures. The changes were accepted by the upstream author of vmdebootstrap yesterday and today, and is now available from the upstream project page.

To use it to build a Raspberry Pi image using Debian Jessie, first create a small script (the customize script) to add the non-free binary blob needed to boot the Raspberry Pi and the APT source list:

set -e # Exit on first error
cd "$rootdir"
cat <<EOF > etc/apt/sources.list
deb jessie main contrib non-free
# Install non-free binary blob needed to boot Raspberry Pi.  This
# install a kernel somewhere too.
wget \
    -O $rootdir/usr/bin/rpi-update
chmod a+x $rootdir/usr/bin/rpi-update
mkdir -p $rootdir/lib/modules
touch $rootdir/boot/start.elf
chroot $rootdir rpi-update

Next, fetch the latest vmdebootstrap script and call it like this to build the image:

sudo ./vmdebootstrap \
    --variant minbase \
    --arch armel \
    --distribution jessie \
    --mirror \
    --image test.img \
    --size 600M \
    --bootsize 64M \
    --boottype vfat \
    --log-level debug \
    --verbose \
    --no-kernel \
    --no-extlinux \
    --root-password raspberry \
    --hostname raspberrypi \
    --foreign /usr/bin/qemu-arm-static \
    --customize `pwd`/customize \
    --package netbase \
    --package git-core \
    --package binutils \
    --package ca-certificates \
    --package wget \
    --package kmod

The list of packages being installed are the ones needed by rpi-update to make the image bootable on the Raspberry Pi, with the exception of netbase, which is needed by debootstrap to find /etc/hosts with the minbase variant. I really wish there was a way to set up an Raspberry Pi using only packages in the Debian archive, but that is not possible as far as I know, because it boots from the GPU using a non-free binary blob.

The build host need debootstrap, kpartx and qemu-user-static and probably a few others installed. I have not checked the complete build dependency list.

The resulting image will not use the hardware floating point unit on the Raspberry PI, because the armel architecture in Debian is not optimized for that use. So the images created will be a bit slower than Raspbian based images.

Tags: debian, english, freedombox, mesh network.
Det er jo makta som er mest sårbar ved massiv overvåkning av Internett
26th October 2013

De siste måneders eksponering av den totale overvåkningen som foregår i den vestlige verden dokumenterer hvor sårbare vi er. Men det slår meg at de som er mest sårbare for dette, myndighetspersoner på alle nivåer, neppe har innsett at de selv er de mest interessante personene å lage profiler på, for å kunne påvirke dem.

For å ta et lite eksempel: Stortingets nettsted, (og forsåvidt også, inneholder informasjon om det som foregår på Stortinget, og jeg antar de største brukerne av informasjonen der er representanter og rådgivere på Stortinget. Intet overraskende med det. Det som derimot er mer skjult er at Stortingets nettsted bruker Google Analytics, hvilket gjør at enhver som besøker nettsidene der også rapporterer om besøket via Internett-linjer som passerer Sverige, England og videre til USA. Det betyr at informasjon om ethvert besøk på stortingets nettsider kan snappes opp av svensk, britisk og USAs etterretningsvesen. De kan dermed holde et øye med hvilke Stortingssaker stortingsrepresentantene synes er interessante å sjekke ut, og hvilke sider rådgivere og andre på stortinget synes er interessant å besøke, når de gjør det og hvilke andre representanter som sjekker de samme sidene omtrent samtidig. Stortingets bruk av Google Analytics gjør det dermed enkelt for utenlands etteretning å spore representantenes aktivitet og interesse. Hvis noen av representantene bruker Google Mail eller noen andre tjenestene som krever innlogging, så vil det være enda enklere å finne ut nøyaktig hvilke personer som bruker hvilke nettlesere og dermed knytte informasjonen opp til enkeltpersoner på Stortinget.

Og jo flere nettsteder som bruker Google Analytics, jo bedre oversikt over stortingsrepresentantenes lesevaner og interesse blir tilgjengelig for svensk, britisk og USAs etterretning. Hva de kan bruke den informasjonen til overlater jeg til leseren å undres over.

Tags: norsk, personvern, sikkerhet, stortinget, surveillance.
A Raspberry Pi based batman-adv Mesh network node
21st October 2013

The last few days I have been experimenting with the batman-adv mesh technology. I want to gain some experience to see if it will fit the Freedombox project, and together with my neighbors try to build a mesh network around the park where I live. Batman-adv is a layer 2 mesh system ("ethernet" in other words), where the mesh network appear as if all the mesh clients are connected to the same switch.

My hardware of choice was the Linksys WRT54GL routers I had lying around, but I've been unable to get them working with batman-adv. So instead, I started playing with a Raspberry Pi, and tried to get it working as a mesh node. My idea is to use it to create a mesh node which function as a switch port, where everything connected to the Raspberry Pi ethernet plug is connected (bridged) to the mesh network. This allow me to hook a wifi base station like the Linksys WRT54GL to the mesh by plugging it into a Raspberry Pi, and allow non-mesh clients to hook up to the mesh. This in turn is useful for Android phones using the Serval Project voip client, allowing every one around the playground to phone and message each other for free. The reason is that Android phones do not see ad-hoc wifi networks (they are filtered away from the GUI view), and can not join the mesh without being rooted. But if they are connected using a normal wifi base station, they can talk to every client on the local network.

To get this working, I've created a debian package meshfx-node and a script build-rpi-mesh-node to create the Raspberry Pi boot image. I'm using Debian Jessie (and not Raspbian), to get more control over the packages available. Unfortunately a huge binary blob need to be inserted into the boot image to get it booting, but I'll ignore that for now. Also, as Debian lack support for the CPU features available in the Raspberry Pi, the system do not use the hardware floating point unit. I hope the routing performance isn't affected by the lack of hardware FPU support.

To create an image, run the following with a sudo enabled user after inserting the target SD card into the build machine:

% wget -O build-rpi-mesh-node \
% sudo bash -x ./build-rpi-mesh-node > build.log 2>&1
% dd if=/root/rpi/rpi_basic_jessie_$(date +%Y%m%d).img of=/dev/mmcblk0 bs=1M

Booting with the resulting SD card on a Raspberry PI with a USB wifi card inserted should give you a mesh node. At least it does for me with a the wifi card I am using. The default mesh settings are the ones used by the Oslo mesh project at Hackeriet, as I mentioned in an earlier blog post about this mesh testing.

The mesh node was not horribly expensive either. I bought everything over the counter in shops nearby. If I had ordered online from the lowest bidder, the price should be significantly lower:

TeknikkmagasinetRaspberry Pi model B349.90
TeknikkmagasinetRaspberry Pi type B case99.90
LefdalJensen Air:Link 25150295.-
Clas OhlsonKingston 16 GB SD card199.-
Total cost943.80

Now my mesh network at home consist of one laptop in the basement connected to my production network, one Raspberry Pi node on the 1th floor that can be seen by my neighbor across the park, and one play-node I use to develop the image building script. And some times I hook up my work horse laptop to the mesh to test it. I look forward to figuring out what kind of latency the batman-adv setup will give, and how much packet loss we will experience around the park. :)

Tags: english, freedombox, mesh network, nuug.
Perl library to control the Spykee robot moved to github
19th October 2013

Back in 2010, I created a Perl library to talk to the Spykee robot (with two belts, wifi, USB and Linux) and made it available from my web page. Today I concluded that it should move to a site that is easier to use to cooperate with others, and moved it to github. If you got a Spykee robot, you might want to check out the libspykee-perl github repository.

Tags: english, nuug, robot.
Good causes: Debian Outreach Program for Women, EFF documenting the spying and Open access in Norway
15th October 2013

The last few days I came across a few good causes that should get wider attention. I recommend signing and donating to each one of these. :)

Via Debian Project News for 2013-10-14 I came across the Outreach Program for Women program which is a Google Summer of Code like initiative to get more women involved in free software. One debian sponsor has offered to match any donation done to Debian earmarked for this initiative. I donated a few minutes ago, and hope you will to. :)

And the Electronic Frontier Foundation just announced plans to create video documentaries about the excessive spying on every Internet user that take place these days, and their need to fund the work. I've already donated. Are you next?

For my Norwegian audience, the organisation Studentenes og Akademikernes Internasjonale Hjelpefond is collecting signatures for a statement under the heading Bloggers United for Open Access for those of us asking for more focus on open access in the Norwegian government. So far 499 signatures. I hope you will sign it too.

Tags: debian, english, opphavsrett, surveillance.
Oslo community mesh network - with NUUG and Hackeriet at Hausmania
11th October 2013

Wireless mesh networks are self organising and self healing networks that can be used to connect computers across small and large areas, depending on the radio technology used. Normal wifi equipment can be used to create home made radio networks, and there are several successful examples like Freifunk and Athens Wireless Metropolitan Network (see wikipedia for a large list) around the globe. To give you an idea how it work, check out the nice overview of the Kiel Freifunk community which can be seen from their dynamically updated node graph and map, where one can see how the mesh nodes automatically handle routing and recover from nodes disappearing. There is also a small community mesh network group in Oslo, Norway, and that is the main topic of this blog post.

I've wanted to check out mesh networks for a while now, and hoped to do it as part of my involvement with the NUUG member organisation community, and my recent involvement in the Freedombox project finally lead me to give mesh networks some priority, as I suspect a Freedombox should use mesh networks to connect neighbours and family when possible, given that most communication between people are between those nearby (as shown for example by research on Facebook communication patterns). It also allow people to communicate without any central hub to tap into for those that want to listen in on the private communication of citizens, which have become more and more important over the years.

So far I have only been able to find one group of people in Oslo working on community mesh networks, over at the hack space Hackeriet at Husmania. They seem to have started with some Freifunk based effort using OLSR, called the Oslo Freifunk project, but that effort is now dead and the people behind it have moved on to a batman-adv based system called meshfx. Unfortunately the wiki site for the Oslo Freifunk project is no longer possible to update to reflect this fact, so the old project page can't be updated to point to the new project. A while back, the people at Hackeriet invited people from the Freifunk community to Oslo to talk about mesh networks. I came across this video where Hans Jørgen Lysglimt interview the speakers about this talk (from youtube):

I mentioned OLSR and batman-adv, which are mesh routing protocols. There are heaps of different protocols, and I am still struggling to figure out which one would be "best" for some definitions of best, but given that the community mesh group in Oslo is so small, I believe it is best to hook up with the existing one instead of trying to create a completely different setup, and thus I have decided to focus on batman-adv for now. It sure help me to know that the very cool Serval project in Australia is using batman-adv as their meshing technology when it create a self organizing and self healing telephony system for disaster areas and less industrialized communities. Check out this cool video presenting that project (from youtube):

According to the wikipedia page on Wireless mesh network there are around 70 competing schemes for routing packets across mesh networks, and OLSR, B.A.T.M.A.N. and B.A.T.M.A.N. advanced are protocols used by several free software based community mesh networks.

The batman-adv protocol is a bit special, as it provide layer 2 (as in ethernet ) routing, allowing ipv4 and ipv6 to work on the same network. One way to think about it is that it provide a mesh based vlan you can bridge to or handle like any other vlan connected to your computer. The required drivers are already in the Linux kernel at least since Debian Wheezy, and it is fairly easy to set up. A good introduction is available from the Open Mesh project. These are the key settings needed to join the Oslo meshfx network:

Protocol / kernel modulebatman-adv
Channel / Frequency11 / 2462
Cell ID02:BA:00:00:00:01

The reason for setting ad-hoc wifi Cell ID is to work around bugs in firmware used in wifi card and wifi drivers. (See a nice post from VillageTelco about "Information about cell-id splitting, stuck beacons, and failed IBSS merges! for details.) When these settings are activated and you have some other mesh node nearby, your computer will be connected to the mesh network and can communicate with any mesh node that is connected to any of the nodes in your network of nodes. :)

My initial plan was to reuse my old Linksys WRT54GL as a mesh node, but that seem to be very hard, as I have not been able to locate a firmware supporting batman-adv. If anyone know how to use that old wifi access point with batman-adv these days, please let me know.

If you find this project interesting and want to join, please join us on IRC, either channel #oslohackerspace or #nuug on

While investigating mesh networks in Oslo, I came across an old research paper from the university of Stavanger and Telenor Research and Innovation called The reliability of wireless backhaul mesh networks and elsewhere learned that Telenor have been experimenting with mesh networks at Grünerløkka in Oslo. So mesh networks are also interesting for commercial companies, even though Telenor discovered that it was hard to figure out a good business plan for mesh networking and as far as I know have closed down the experiment. Perhaps Telenor or others would be interested in a cooperation?

Update 2013-10-12: I was just told by the Serval project developers that they no longer use batman-adv (but are compatible with it), but their own crypto based mesh system.

Tags: english, freedombox, mesh network, nuug.
Skolelinux / Debian Edu 7.1 install and overview video from Marcelo Salvador
8th October 2013

The other day I was pleased and surprised to discover that Marcelo Salvador had published a video on Youtube showing how to install the standalone Debian Edu / Skolelinux profile. This is the profile intended for use at home or on laptops that should not be integrated into the provided network services (no central home directory, no Kerberos / LDAP directory etc, in other word a single user machine). The result is 11 minutes long, and show some user applications (seem to be rather randomly picked). Missed a few of my favorites like celestia, planets and chromium showing the Zygote Body 3D model of the human body, but I guess he did not know about those or find other programs more interesting. :) And the video do not show the advantages I believe is one of the most valuable featuers in Debian Edu, its central school server making it possible to run hundreds of computers without hard drives by installing one central LTSP server.

Anyway, check out the video, embedded below and linked to above:

Are there other nice videos demonstrating Skolelinux? Please let me know. :)

Tags: debian edu, english, video.

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