New git frontend

Trying to move from gitlab source installation to omnibus failed miserable. Despite spending a whole day, I didn’t got it running. Obstacles have been the migration of the complex setup and disk space consumption. It is just a small VM running the klostercluster Web page.

Just by accident I found a review of gogs. Looks very nice, is simple to setup, well, the apache2 proxying with sub-url took some time, but beside this it was an easy exercise. The set of features is fully sufficient and the whole thing is much more stable and much much more faster. Let’s see if this promising start develops into a long-term experience.

New 48 port CISCO switches

We got four 48 port manageable CISCO switches from dataport. This switches offer a lot of possibilities to improve the network situation for working with the cluster.

We are getting independent of the network of the school!

The fact that the switches are manageable means the same time that we have to manage them. So, a view things have to be learned.

However, connecting to the switches for initial setup requires a classical serial line. As those are not made available on all of the accessible computers a DIY solution is required.

The following figure shows the diagram for building a converter to attach the switches serial interface to a RaspberryPi.


A manual for working with the serial interface on the RaspberryPi can be found on the materials page.

For further reference: the layout of the RaspberryPis GPIO and the DB9 connector.




The cluster is up and running

Some impressions on the current results and work in progress.

Since today all cluster nodes are up and running. Firmware and operating system updates have been performed and the administrative ssh key is distributed. NExt step is to enable LDAP and the nfs home directories on the compute nodes. This setups can be distributed via scripts.

This group is working on analyzing the numerical convergence properties of their version of the daisyworld:


This is work done towards a temperature measurement driven air condition control unit:



Distribution of the administrators ssh keys on the cluster nodes for the distributed shell:


And here are two pictures of the cluster:


Note the custom designed power distribution boards:


Pupils exchange and starting the cosmic ray muon detector

During the last week a group of pupils from Istanbul in Turkey have been visiting the Physik-Profil of the Klosterschule and started the muon detector for the Kulturnacht.

If you like to find out more on the muon detector, you could visit:

The cosmic ray muon detector e-lab site.

Today we have been visiting the Town Hall of Hamburg and finally we made some photos of the whole group.


Lötübung, 2013-09-19

Hier sind zwei Bilder unseres Lötkurses:

Im ersten Bild sind zwei saubere Lötstellen. Die eine noch mit Draht und die andere bereits mit abgeschnittenem. Die Form des Lötzinns entspricht genau der geforderten. Um die Farbe des Lötzinns erkennen zu können, sind die Farben des Fotos leider nicht gut genug. Sie entsprechen der Vorgabe.


Im zweiten Bild ist im Zentrum eine kalte Lötstelle zu erkennen. Das Lötzinn verbindet nicht den Draht im Loch mit der kupfernen LEiterbahn auf der Platine. Hier wird kein Strom geleitet. Ursache ist ein mangelndes Erwärmen des Drahtes gleichzeitig mit dem Kupfer der Leiterbahn.


Development plan 2nd stage

We have been proceeding with developing the cluster project. On the software side we made some progress. I collected all results. However, it has been pointed out that the basic knowledge on electrical circuits and all stuff around is too limited. So we started with a lecture and experiments on the particular basics. The handout of the lecture is available in Materialien.

The outcome of the brainstorming on the cluster’s software:


How to create a ssh key

You can use SSH keys to establish a secure connection between two computers. The steps below will walk you through generating an SSH key.

Step 1: Check for SSH keys

First, we need to check for existing ssh keys on your computer. Open up a terminal and run the following command to list the files in your .ssh directory:

cd ~/.ssh

Check the directory listing to see if you have a file named either or If you don’t have either of those files proceed with step 2. Otherwise, you already have an existing key pair, and you do not need to do anything.

Step 2: Generate a new SSH key

To generate a new SSH key, enter the command below. We want the default settings so when asked to enter a file in which to save the key, just press enter, but do not omit setting a passphrase (a password) for the key.

ssh-keygen -t rsa -C ""

Why do passphrases matter? It keeps your secret key part secret and prevent its usage in case some can copy it!

As a result you get something like:

# Your identification has been saved in \$HOME/.ssh/id_rsa.
# Your public key has been saved in \$HOME/.ssh/
# The key fingerprint is:
# 01:0f:f4:3b:ca:85:d6:17:a1:7d:f0:68:9d:f0:a2:db