Topic: Computer

Hardware, software & hacks

Monitor test

Sometimes I need to check the function and picture quality of displays. Usually this is done by using some kind of test software – but you can not always install or run software, for example when Linux is installed but the test software is only available for Windows.

For this reason (and because I wanted to learn more about using canvas elements in HTML5 and High DPI displays) I created a test page which uses a canvas element and JavaScript to create a number of test pictures. See “Monitor test” in the “Tools” menu.

In the latest version I also fixed some problems for full screen mode, so every modern browser should be usable for the test.

Jim Austin’s computer sheds

In August 2017 I had the opportunity to meet Prof. Jim Austin and visit his “computer sheds”. Jim Austin is a professor of computer science and has a very extensive, private collection of computers that he has collected in his warehouses over many years.

The collection is not (yet) a regular exhibition, but if you register in advance, you can get a private tour for a little donation. Also see Below is a loose collection of pictures I took during my visit.

My special thanks go to Jim Austin and Trevor Howard-Smith for the friendly guidance and to the many people helping with cataloging and preparing the collection!

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Pebble still useable

The Pebble is offically dead  since the end of 2016 where Fitbit bought the software and the production of the hardware was discontinued.

But this does not mean that the existing copies don’t work any longer – Fitbit will turn off the cloud services by the end of 2017 but there is a new version of the Pebble App already available since April 2017 which does not require a cloud connection. Apps which are already installed on the Pebble and which don’t need a cloud connection can still be used. Also side loading of new apps is still possible as in “Nav Me” or “Pebble Camera”.

So my Pebble will still be usable until I got an alternative :-).

Update August 2017

Unfortunately the latest version of the Pebble app turned out not to be very reliable. Therefore I changed to a Samsung Gear S3.

Good bye Pebble :-(

Now it’s official: Pebble shuts down and the remaining stuff will be sold to Fitbit as you can read in the blog post. Pebble Time 2 or any of the other announced products will not be available at all.

Very sad – since I just bought my first Pebble in the beginning of 2016 and was always very pleased so far. The battery still lasts more than a week and besides notifications about new SMS or e-mails I also really like apps like “Nav Me” – as long as it will be possible.

Postgrey doesn’t start

Recently I’ve noticed that greylisting didn’t work any longer on my server. The reason for this was, that the service “postgrey” did not start any longer.

A manual start using the command line was still possible but not starting it as daemon.

A quick fix for this is to modify the file /etc/sbin/postgrey as following: change the shebang in the first line.


#!/usr/bin/perl -T -w


#!/usr/bin/perl -w

However this also makes the script less safe as well. The better solution is a modification of the script as described on

Also see

TLS with Let’s Encrypt

From now on I use TLS certificates by Let’s Encrypt for all my services (web, e-mail, XMPP etc.).

This is not a classic certification authority (CA) but an initiative which was originally founded by Mozilla, the EFF and the University of Michigan and is now provided by the Internet Security Research Group (ISRG). The goal of Let’s Encrypt is it to provide encryption everywhere by offering the required certificates for free. Since April 2016 Let’s Encrypt is not beta any longer but officially in operation.

To use Let’s Encrypt a client is required which renews the certificates via the “ACME” protocol on a regular basis as the certificates are only valid for three months. For this I use the shell script getssl with which you can automate the process very easy. This script will be executed with a cron job once a day to check the age of certificates and renew them. It will also tell the affected services to reload their configuration or restart the affected services if required.

Vintage Computing Festival Berlin 2016

In October 2016 I participated the Vintage Computing Festival Berlin ( for the first time – with my old Atari 1040STe which still works fine even after 20 years. This is especially impressive for the harddisc.

Atari 1040 STe on the VCFB 2016

There I showed how I developed my alternative desktop “Thing” and I explained the programs which I used for that (PureC, Interface, Everest and others).

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