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Andreas 'ads' Scherbaum

The Raspberry Pi with the touch display for the home automation system is coming along nicely. One problem to solve: how to display the openHAB HABpanel, and which browser to use?

Firefox and Chrome don't run on Raspbian. However "Chromium" (the open source part of the Chrome browser) is. That's a good start. But how to start the browser automatically, and in full screen?

Andreas 'ads' Scherbaum

Recently I installed a Raspberry Pi with Raspbian, and attached a touchscreen to it. The device is supposed to work as a display for our openHAB home automation system. All nice and shiny, except the Pi occasionally disconnects from the Wi-Fi - apparently in order to safe power. Once the network device is needed, the Wi-Fi is reconnected. That is the default setting.

That is quite annoying, because the HABpanel will lose it's connection to the openHAB server, and no longer show widget updates. Some widgets like "time" will just continue to work, but other widgets like status of the washing machine, or the current outside temperature just show the last state, and never update.

Andreas 'ads' Scherbaum

GNU parallel allows you to multiplex tasks, and possibly use more CPU resources to speed up the task at hand. This works if your task can be split down into multiple independent tasks which otherwise will be executed serially.

An example: you find files in a directory, and want to compress all of them:

find /path/to/directory -type f -exec bzip2 -9 {} \;

Above line will find all the files, and compress each of them, one after the other. Most modern systems have multiple CPU cores installed, but nevertheless above line will only use one of them. GNU parallel solves this by multiplexing the task, and starting multiple compress processes. Above line changes to:

find /path/to/directory -type f -print0 | parallel -0 --no-run-if-empty bzip2 -9 :::

By default, parallel will start as many parallel processes as CPU cores are available. The --jobs option can be used to specify a hardcoded number (as example: "8"), or limit the number depending on the number of available cores ("-2" will start 6 processes if 8 cores are available, "+2" will start 10 processes if 8 cores are available).

However when you start "parallel", it will nag you that you confirm that any time you use it for processing data for an academic article, you have to cite "parallel":

Academic tradition requires you to cite works you base your article on.
When using programs that use GNU Parallel to process data for publication
please cite:

  O. Tange (2011): GNU Parallel - The Command-Line Power Tool,
  ;login: The USENIX Magazine, February 2011:42-47.

This helps funding further development; AND IT WON'T COST YOU A CENT.
If you pay 10000 EUR you should feel free to use GNU Parallel without citing.

To silence this citation notice: run 'parallel --citation'.

That's ok if you use it manually, but in a server environment no one will ever see this note.

Andreas 'ads' Scherbaum

Most of my systems run on a software RAID 1 configuration (that is, two disks, where each disk is mirrored to the other). This way, one of the disks can fail and still all the data is available.

If a disk failure happens, the disk is replaced with a similar disk, and then needs to be configured and re-added to the RAID.

Newer systems all use the GUID partition table (GPT), and therefore allow almost unlimited disk sized. Instructions for re-adding a disk using GPT are a bit different from the days when MBR (up to 2 TB disk space) was used, therefore I'm writing them down here for future use.

Andreas 'ads' Scherbaum

A while ago I asked for recommendations for Android Podcast apps. From all over the Internet I got a great number of recommendations, and looked into all of them.

Andreas 'ads' Scherbaum

While diving deeper into my openHAB installation, the need for notifications on mobile phones came up. After some research, I settled with Pushover, which provides Android and iOS apps, as well as Desktop notifications. openHAB Rules have support for Pushover, and everything works well together.

Except when Android decides to kill apps, because they sit idle and do nothing. It so happens on my Huawei phone that notifications are delivered to the device, but no popup shows up. Only when I open the up, suddenly all the messages are there. The Pushover FAQ has an entry for this, even for Huawei phones, but it is outdated.

Andreas 'ads' Scherbaum

Ansible comes with a plugin which allows to create and renew Let's Encrypt certificates. Documentation is sparse, so I decided to post about my own Playbook.

Andreas 'ads' Scherbaum

Up until recently I was using an App to clean the the Android cache once in a while. If you don't, the device over time get's sluggish, because too many apps store too much data in the cache. Over time this cache can grow to GBs in size.

On the other hand, every single "clean cache App", over time, started showing more and more aggresive advertising. I get that the developer wants to make some money, that's fine. But maybe the money is not enough, so more advertising it is.

Turns out, there is a built-in way in Android to clean the cache. No need for an extra App.

Andreas 'ads' Scherbaum

Recently it was time to refurbish our email infrastructure. For a very long time I was hosting everything for myself, but things don't get easier and over time even the spam filters couldn't catch up. Therefore I looked into a number of hosted services, and in the end settled with Google Gmail.

Andreas 'ads' Scherbaum

Recently smplayer (not mplayer) started behaving strange: every video started muted. Pressing the mute button (m key) really muted the sound, pressing the button again unmuted the sound and the audio started playing. This behavior persisted over restarts of smplayer.

Now that is really annoying!