• I didn’t choose the Geode GL/GX last time, doh!
• The kernel is no longer tickless (performs better)
• Threw out some modular crypto-stuff (which I missed the last time)

There are three front-LEDs on the ALIX board, so nothing fancy. The interesting is that there are predefined triggers for these LEDs in /sys/class/leds/ which will make the LEDs display one of the following: heartbeat = load average (blinking speed), ide-disk (write access to the cf-card), timer, etc. Just try cat trigger to see the possible values. There is also the possibility to trigger on matches from iptables (think: traffic on port 22 ;). However my iptables userland seems to be outdated, so I will have to report about this another time.

Furthermore I tried using lighttpd instead of gatling on my fat external drive, and it performed even better, using slightly less CPU. In the kernel I activated the deadline IO-scheduler as default (while keeping CFQ and NOOP as an option), let’s see how that plays out. I’m still not getting more than 9MB/s using Samba, while the CPU is mostly idle and lighty completely saturates the 100MBit link, really annoying.

lm_sensors on the ALIX are no problem either. Just try my kernel-config or make sure to activate the basic I2C-stuff and CONFIG_SCx200_ACB. My ALIX runs at comfy 42°C when not under load.

I already talked about using tmpfs for some of the directories written to frequently (/tmp, /var/tmp, /var/run, /var/log, /var/lock). I don’t care about logs right now, so I don’t mind losing them on reboot. Some daemons however complain or won’t start if their log-directories aren’t set up, so you should do that with an init-script. I uploaded my script here, which will work with Debian and also sets up two LEDs and the deadline scheduler in case it isn’t the default.

Specs
PCEngines has an overview over the ALIX-line as well as the specs of the ALIX 2D13, so this is just a short rundown:

• 500 MHz AMD Geode LX800 (x86)
• 256 MB DDR DRAM
• 3 Ethernet NICs (Via VT6105M 10/100)
• Furthermore: 2x USB ports, MiniPCI-slot, CF-slot, serial port

I chose the 2D13 model since I wanted 3 ethernet NICs and the added battery (for keeping system time after a reboot) seemed like a good idea. The ALIX boards can be bought in many variations, some even providing VGA/sound to be used as a thin client. I ordered my ALIX at the Varia-Store, where they offer a complete bundle of ALIX-2D13-board, enclosure, power supply and CF-card for a mere €145 including shipping in Germany. I ordered on Tuesday at noon and the package arrived Thursday afternoon.

Operating system / prerequisites
You probably want to run Linux on these babies, otherwise you can stop reading ahead. There are some things you really need before you get started:

• CF-card reader on your computer (for installing the OS to the CF-card)
• Serial connection (think USB-to-Serial converter, pl2303) to access the ALIX

I chose to install Debian on the ALIX, since I’m familiar with it and it has little overhead. I found these guides to be helpful, even if not completely up to date or correct: Guide 1, Guide 2. But careful! Don’t mount the ALIX board in its enclosure until you’re sure that your ALIX boots, since removing the CF-card requires taking the board out again ;).
The next thing I did was to build a custom kernel, since Debian only includes 2.6.26 and has everything you’ll never need compiled as modules. I built a next-to-minimal kernel on my workstation (this site helped a lot) and it seems to work just fine so far. The config is here. An important thing if you compile somewhere else is to make sure you useARCH=i386 make menuconfig
ARCH=i386 make -j3 when configuring and compiling your kernel for the ALIX.
People already using CF-cards or small embedded devices probably know to use noatime where possible and mount /tmp, /var/tmp, /var/run, /var/log, /var/lock as tmpfs to go easy on the CF-cards limited write cycles.

Performance / Applications
I bought the ALIX to play around with it but also to evaluate its possible use as a Samba-fileserver and CUPS printserver for my flat, and maybe even a small shellserver in case I’m away from home and my workstation isn’t running. With an energy-consumption of about 5-6W you can have it running 24/7, the fact that it doesn’t have any moving parts only adds to that. Booting takes a few seconds by the way, not that it matters.

The first measurements I did were with scp from the ALIX to my WS, which maxed out at 3.5MB/s because OpenSSH used up the CPU on the ALIX. Next I tried using Samba (to and from) and got a mere 6.5MB/s throughput reading from the ALIX and an attached USB-drive. This was with the stock kernel however, and using my own 2.6.34-kernel I was able to transmit more than 9MB/s using Samba. I had a stupid line in my smb.conf which might explain the 6.5MB/s I got before. Make sure to remove this line!:socket options = IPTOS_LOWDELAY TCP_NODELAY SO_RCVBUF=16384 SO_SNDBUF=16384I then did another test using fefes gatling web/ftp/samba-server on the ALIX and my USB-drive in HTTP-mode with wget and was able to completely saturate the 100MBit-link, which is why I suspect to be able to do the same thing with Samba as well.
For customers of Aachens Uni-DSL it should be interesting to know that I managed to max out my 8Mbit-DSL-line (about 700kB/s) using vpnc on the ALIX with enough idle CPU left. Using vpnc and doing a git pull on the ALIX resulted in only a slight slowdown since git was busy saving/packing objects it received. Performance using git daemon on the ALIX and pulling from there were acceptable as well.

All of these measurements are highly unscientific and side-effects or misconfigurations could have had negative effects, so one should read these rates as minimal assurances.

Conclusion
After the first full day of using the ALIX I’m impressed. The CPU is powerful enough for most tasks and with a little custom configuration some things can be sped up considerably. I don’t see any problems for the intended use as a file-server, by whichever way the files are served. The next step will be hooking up my printer.

If you intend to use encrypted filesystems on the ALIX you should do some research first. While the AMD Geode does have hardware support for AES, OpenSSL does not seem to use it and I’m not quite sure about any cryptofs. Another common thing the ALIX might be used for is wireless LAN. The MiniPCI-slot can take a variety of wireless NICs, but I don’t need yet another AP at the moment.

Photography
You accidentally selected “Delete All” on your digital cameras and now your photos are gone? You even fear they might have been overwritten by photos taken after the accident? Fear not, the same thing happened to me, and I was able to restore all the photos from the event plus photos going back as far as three months from my CF card in my 400d using the PhotoRec software.

Cameras today often have an orientation sensor, so pictures taken in portrait mode will automatically be rotated. But this usually happens in the viewer, while the orientation is simply an EXIF tag. Of course this takes up precious computing time and not every viewer supports it. jhead can not only display EXIF information in a consistent manner but can also rotate pictures lossless and clear the orientation-tag afterwards. The call is jhead -autorot *.JPG
If you want to rename your images using EXIF-information, exiftool is the way to go. The command exiftool '-FileName<Party_ ${CreateDate}_${filename}' -d %Y%m%d *.jpg would prefix all the photos with “Party” and the create-date, while keeping the original filename as the suffix. exiftool can shift dates too, if you ever forget to adjust for daylight saving.

When uploading the images you’ll often want to resize them. The ImageMagick collection can do just that, and many other things (like sharpening etc.). If you mogrify -resize 1600x1600 your photos will be resized to 1600px maximum edge length, while keeping the ratio. But be careful, mogrify overwrites the pictures in place!

Music
Thanks to services like video2mp3.net/ you can download a lot of music from YouTube. But sometimes there is silence at the end or the beginning of a song, and a whole collection of songs might have differing levels of volume. To cut an mp3 you can use mp3splt like this to cut everything after 03:30 minutes:mp3splt file.mp3 00.00 03.30The sound levels can be normalized, losslessly, using mp3gain:mp3gain -rk *

Misc
When pretty-printing flat text files I use a2ps to format them nicely and get a PostScript-document. a2ps however does not support UTF-8, while the only characters I care about (German Umlauts) can be represented using Latin1 just fine. So, one can use iconv to convert them on the fly like this:iconv --from-code=UTF-8 --to-code=LATIN1 textfile.txt|a2ps --font 9 -E -B -r --column=1 > out.ps

To export images from a PDF-file I discovered pdfImages, which is part of the xpdf-suite. Use it like this:pdfimages -j foo.pdf bar

Believe it or not, this photo was taken about 2km from my parents home, from the dam of the Eschbachtalsperre, a dam for providing the region with drinking water. Usually I just jog around the lake in the morning, but last weekend Katrin and I discovered one of multiple hiking routes around it and the surrounding area. The trails all start at the parking lot and are clearly marked along the way.

I uploaded this shot along with other shots to flickr, but then decided to go back and give it a little more depth in Gimp (using Contrast/Saturation, Sharpen, a Tone-Mapping plugin and a gradient for the sky).

The shot on the left was done after Katrin asked me for some photos to illustrate a blogpost related to medicine over on her blog. Some other site apparently had the same idea, and now this photo can be found here, here, here and here. This was not only rewarding for me but also interesting since I discovered (from this and other shots) that websites not only seem to search flickr but rather other related articles on related websites and simply use the same photos. When the photo is used in the right context and the website itself looks professional, one might even forget the small “CC by heipei” link at the bottom and the fact that I’m an amateur spending little time or effort (much less creativity ;) on these shots. This can only lead to the conclusion that photography is as least as much simple engineering as creativity, or that I have some hidden sense for compositing an image resulting from years of experimentation, browsing flickr and doing CG where you spend a lot of time making your rendered images look like photographs.

In general I’m still happy with my EF-S 18-200mm 3.5-5.6 and my EF 50mm 1.4, and the decision to buy a Speedlite was absolutely right (in fact, reviewing old shots, I’ve been kicking myself about not having bought one earlier). Apart from some crazy experiments and time-consuming handicrafted tools, my usual approach is to use the flash pointed toward the ceiling, increase it 1/3 to 1 with TTL and just fire away. If possible, a natural balance with available light will make laymen forget a flash was even used. You can go fully manual or simply use the ‘P’-mode with an appropriate aperture. A nice result can be seen on the right, though Katrin is slightly underexposed in this one. What I did was take the photo indoors (where you have your trusty white ceiling) in front of an open window at dusk. The backlight was provided by the setting sun, which adds a lot the shot and usually is done with a dedicated flash. I will be trying more of these in the future.

A little photostream-recap below, so no one can complain that I’m not blogging for the average reader anymore. Enjoy!

Was ist UROP?
UROP, das Undergraduate Research Opportunities Program, ist ein Förderungsprogramm für Studenten. Wie der Name verrät richtet es sich an Undergraduates, also auf das neue BA/MA-System bezogen auf Bachelor-Studenten. Das Research im Titel bezieht sich darauf dass einzelne Forschungsprojekte gefördert werden sollen. Es ist kein Research-Grant in dem Sinne wie man es vielleicht kennt: Mittel für ein Projekt beantragen und dann loslegen. UROP fördert Projekte nach ihrem Abschluss (wenn sie denn erfolgreich beendet wurden) und nach einer Evaluation der fertigen Arbeiten. Das bedeutet allerdings auch nicht dass man sich die Förderung wie ein Wettbewerb vorstellen soll bei dem die besten N Beiträge ausgezeichnet werden.

Ablauf
Wenn man ein Projekt gefunden hat und angenommen wurde kann man loslegen. Ob allein oder im Team ist prinzipiell egal. Zuerst muss man ein paar formale Dinge erledigen: Anschreiben, Lebenslauf, Motivationsbrief. Der Projektzeitraum ist sehr flexibel (ob ein ganzes Jahr oder nur ein paar Wochen), allerdings gibt es nur halbjährlich die Möglichkeit eine Förderung zu beantragen. Man hat einen Betreuer am Lehrstuhl mit dem man regelmäßig den weiteren Verlauf abspricht. Hat man das Projekt beendet schreibt man noch einen dreiseitigen Abschlussbericht und hält eine kurze Präsentation im Zuge des halbjährlichen UROP-Kolloquiums. Vom Betreuer (bzw. Prof. am Lehrstuhl) wird dann auch noch eine Evaluation geschrieben die direkt an UROP geht. Noch ein bisschen Papierkram und man ist fertig. Zuletzt wird das Projekt bewertet (von anderen Profs im eigenen Fachbereich) und wenn alles stimmt erhält man die Förderung (max. 2000€ pro Projekt).

Warum sollte man an UROP teilnehmen?
Das ist eine gültige Frage, kriegt man doch selbst in den einfachen HiWi-Jobs mit 8h/Woche immerhin mehr Geld, rein auf die Arbeitszeit bezogen (hey, das ist nicht meine Argumentationsweise aber solche Sachen wurde ich teilweise gefragt). Allerdings arbeitet man dabei nicht unbedingt so flexibel (was die Zeiteinteilung angeht) und zielorientiert. Wenn man nicht grade an einem guten Lehrstuhl eine Stelle bekommen hat fehlt evtl. sogar der wissenschaftliche Aspekt der Arbeit gänzlich. Die Menge der Leute die sich über das Studium beschweren weil man, selbst in Seminararbeiten oder Praktika, nur bereits Bekanntes zusammenfasst ist groß genug, so dass ich da ein gewisses Interesse vermute. Über ein UROP-Projekt kann man gut mit Mitarbeitern am Lehrstuhl in Kontakt kommen, nicht unwichtig für die spätere Wahl bei der Diplom/Master-Arbeit oder sogar bei weiterführenden Plänen (zugegebenermaßen kann man solche Kontakte natürlich auch unabhängig aufbauen, so gern sich auch alle Veranstaltungen rund um die Uni “Networking” auf die Fahne schreiben). Darüberhinaus schadet es sicherlich nicht ein abgeschlossenes UROP-Projekt auf dem Lebenslauf zu haben.

Warum mache ich Werbung dafür?
Wie gesagt, ich find es schade dass so wenig Leute überhaupt von UROP mitgekriegt haben. Die Fördertöpfe (übrigens im Rahmen der Exzellenzinitiative geschaffen, für alle die meinen dass Studiengebühren auf keinen Fall wieder zu den Studenten zurückfinden) sind voll und es gab bei den letzten vier UROP-Runden weniger Bewerber als Stipendien. Was das Kolloquium angeht waren die Vorträge der anderen UROP-Projekte sehr interessant. So haben wir erfahren dass manche Insekten zwar an Scheiben kleben können, um den Gefrierpunkt aber plötzlich ihre Haftfähigkeit verlieren (das ist mal über den Tellerrand geschaut für Informatiker! ;) Inzwischen gibt es sogar UROP Abroad, ein Programm mit dem man ein UROP-Projekt in den USA/Kanada verfolgen kann. Das hat bisher nur eine Person gemacht, aber die war immerhin im schönen Saskatchewan.

Wo kann man sich informieren?
Am besten auf der RWTH UROP Seite. Dort ist auch die Projektdatenbank verlinkt. Allerdings sollte man sich davon nicht abschrecken lassen. Am besten ist man spricht mit einem Assistenten oder Prof ob er nicht ein Projekt hat was gut in den Rahmen von UROP passen würde.

Image credit: RWTH UROP website

Seminare
Seminare bei uns in der Informatik funktionieren wie folgt: Man bewirbt sich auf ein Seminar zu einem groben Überthema bei einem der Informatik-Lehrstühle. Wenn man Glück hat kriegt man den Platz seiner ersten Wahl. Vor dem Semester sucht man sich dann eins der Themen aus und kriegt ein oder mehrere Paper auf denen man aufbauend seine Seminarausarbeitung schreiben soll. An der Stelle merkt man schon dass der Anteil origineller Arbeit beschränkt ist, was durchaus so vorgesehen ist. Ziel eines Seminars ist es schliesslich sich selbstständig in ein Thema einzuarbeiten und das Ganze dann in einen wissenschaftlich aussehenden Artikel zu gießen. Dafür hat man ein paar Monate Zeit, am Ende gibt es dann ein paar Tage lang Vorträge an denen man sein Seminar den anderen Teilnehmern vorstellt. Ich habe im Hauptstudium zwei Seminare gemacht (und ein Praktikum):

• Praktische Informatik: The most efficient SHA-1 attacks (Prof. Meyer) – Ausarbeitung und Slides
• Theoretische Informatik: Das Cross-Section-Theorem und nicht-mehrdeutige Transducer (Prof. Thomas) – Ausarbeitung und Slides

Prüfungsprotokolle
Bei uns im Hauptstudium schreibt man keine Klausuren mehr (abgesehen von ein paar Scheinklausuren) sondern hat mündliche Prüfungen. Manche Leute schreiben Gedächtnisprotokolle einer Prüfung, damit sich andere besser auf die Atmosphäre bei solchen Prüfungen und den Tiefgang vorbereiten können, den eigentlichen Stoff der abgefragt wird sollte man ohnehin komplett drauf haben ;)

• Protokoll Theoretische Informatik: Angewandte Automatentheorie, Unendliche Spiele, Automaten auf unendlichen Wörtern, Cryptography I + II (Prof. Thomas, Prof. Mathar) – Protokoll
• Protokoll Praktische Informatik: Datenbanken, Logic of Knowledge Bases, Logikprogrammierung (Prof. Lakemeyer) – Protokoll
• Protokoll Vertiefung: IT Security I + II, Massively Distributed Systems I, Communication Systems Engineering I (Prof. Wehrle, Prof. Meyer) – Protokoll

UROP
Zusätzlich haben Flo und ich noch an UROP teilgenommen, dem Undergraduate Research Opportunities Programme der RWTH. Für UROP werden Projekte in unterschiedlichen Fachbereichen ausgeschrieben auf die man sich bewerben kann um dann schon während des Studiums erste Schritte im wissenschaftlichen Arbeiten zu machen. Unser Projekt, welches wir am LuFG Informatik 4 – Distributed Systems Group (Prof. Wehrle) durchgeführt haben hieß ALPHA – An Adaptive and Lightweight Protocol for Hop-by-Hop Authentication. Dabei ging es darum ein Protokoll zu implementieren (und zu erweitern), mithilfe dessen Netzwerkpakete an jeder Stelle im Netzwerk auf Integrität geprüft und ggf. direkt verworfen werden können, z.B. um mobile Endgeräte vor falschem Netzverkehr zu schützen der sonst die Resourcen (CPU und damit auch Batterie) dieser Geräte beanspruchen würde. Zu UROP werde ich bald noch einen eigenen Artikel schreiben. Für UROP mussten wir eine kurze Ausarbeitung schreiben, mit ein bisschen Hintergrundwissen sollte man das Prinzip von ALPHA verstehen.

• Implementation and Improvement of ALPHA: Ausarbeitung für UROP und Slides des UROP Kolloquiums
• ALPHA – An Adaptive and Lightweight Protocol for Hop-by-Hop Authentication: Das Original-Paper auf dem das Protokoll aufbaut

Bei Fragen oder Verbesserungsvorschlägen könnt ihr euch wie immer gern bei mir melden.

Reusing a connection
Anyway, today I wanted to present another advanced feature, one I only stumbled upon while learning for an upcoming exam. The slides mentioned the possibility to share connections on one SSH-channel (to the same destination, obviously). Now, why do you need more than one connection in the first place? Well, sometimes you just need the space, and using screen just doesn’t cut it. Or you use git or scp to the same host you’re logged in already interactively. In that case, you just have to establish one connection and any further connection will use the first one. The benefit? Login is way faster, almost instantly, because the whole handshake and authentication doesn’t have to take place again. The caveat: You’ll have to close your master-connection last, otherwise the other connections will drop too. For me that’s no problem, since the host I use most of the time is also the host I’ve got a session open with 24/7 (IRC).

I’m just gonna show the fully automated version here, though you can use it manually as well, just when you need it. A better description can be found here. To automate it, put this in your ~/.ssh/config (you don’t have a config yet? shocking!):
ControlMaster auto
ControlPath /tmp/%r@%h:%pAs usual, you can put it at the very top to apply for all hosts or you can activate it for specific hosts by putting below a Host declaration. Now all you have to do is use ssh host as usual. You’ll see it’s working when you terminate the connection:
Shared connection to host.de closed.

Reverse tunnel
Yes, you can tunnel with OpenSSH. You can even have it act as a SOCKS proxy, which is really neat when combined with Firefox-plugins like FoxyProxy. But you can also reverse-tunnel your way out of a closed network (or NATed network for that matter) when you don’t have access to any intermediate host (like the router/firewall). It’s easy:
ssh -NR 12345:localhost:22 home.deThis assumes you’re issuing the command from the machine that you want to access (from home) later on. It will bind the port 12345 on home.de so that it is forwarded to port 22 (SSH) on the local host. Yeah, it requires some reverse thinking too to get it right ;) The -N-switch prevents a login, by the way. Obviously it is of little use if your home.de has a flaky dialup connection, so you might want to reverse-tunnel to a stable endpoint (or use something like autossh).

A few weeks ago I decided to finally buy a flash. I didn’t hesitate long and bought the Canon 430EX II. Before that (and while waiting for DHL) I read a lot of strobist.com, so that I hit the ground running when the flash did arrive. The nice thing about buying flashes is that you don’t have to worry so much about capabilities/size, because you can buy a bigger one which can act as master at some point in the future should you feel the need to. Along with the flash I ordered some small utilities, like the Phottix Tetra radio-triggers for off-camera flash, the Roscoe Strobist Gel collection (gel from “gelatine”. It’s called “Effektfolien” in german) and a small diffuser (just for fun). The Phottix Tetra have been great as well, especially considering the price-tag of about 30€, which is next to nil compared to other wireless triggers which quickly add up to ten times that much. However the Phottix triggers don’t support TTL, which is a measuring-system so the camera knows how to adjust for the flash. Well, what better time to really get acquainted with the M mode ;)

Aachen Open 2010, which just ended today, was the only real event I looked forward to, photography-wise, and it turned out really nice. Not only was the event itself a smashing success (no other way to put it, the organisation was flawless, the attendance was record-breaking and the venue perfect for our needs), but also meant many diverse personalities to photograph. You can see my complete photos of the event here: photos.heipei.net/Aachen_Open_2010/ and photos by other people will be collected here: http://cube.hackvalue.de/ao10/media-de.

Tonight I salvaged an old (and broken) Umbrella and simply covered the inside with white xerox paper. I sawed of the round part of the handle and now it fits into the grip of my tripod. The Phottix has a mount option for standard tripods. The results are amazing, and as usual I now feel much better when I buy an umbrella (I’m not quite sure whether I want reflective or shoot-through or both ;)