Dec 27, 2021

Running a movie on an external DVD drive on a Chromebook (like HP x360)

In a first step this task sounds very easy:

  • watch a DVD on a chromebook

But...

What are the problems?

  1. Using an external drive to access the dvd
  2. No appropriate app available in play store or chrome web store

There are different solutions out there. 

  1. Convert the DVD to a mp4 and watch this
  2. Use VLC from play store --> does not recognize the DVD
  3. Use VLC from chrome web store --> does not start at all
  4. Use linux development environment

Option 4 seemed to me as the most promising way to go.

Setting up linux is very easy:

 After that you have a debian bullseye running inside a container. Go to /etc/apt/sources.list and add "contrib" after "deb https://debian.org/debian bullseye main " ("sudo bash" to get root). Then 

apt update
apt upgrade
apt install vlc libdvd-pkg
dpkg-reconfigure libdvd-pkg

After that vlc is configured including the libdvdcss for the DVD region codes.

One last problem is to access the DVD inside this linux container. This can be done via a double tap inside the file-manager on the chromebook and then you can choose inside the context menu "share with linux (Mit Linux teilen)".

This last step has to be done each time a DVD is inserted. 

So watching DVDs on a chromebook is not impossible, but it is not really user friendly...


Dec 4, 2021

influxdb: copying data with SELECT INTO - pay attention to the TAGS (or they are transformed to fields)

 If you are using influxdb, one usecase could be, copy the data from a measurement ("table") to another.

This can be done with this statement:

select * into testtable2 from testtable1

By the way: the CLI is opened with

/usr/bin/influx -unsafeSsl -ssl -database telegraf
(if your database is named telegraf)

In my case (zigbee / mqtt / telegraf) the layout of mqtt_consumer measurement was like this:

> show tag keys from mqtt_consumer
name: mqtt_consumer
tagKey
------
host
topic
> show field keys from mqtt_consumer
name: mqtt_consumer
fieldKey    fieldType
--------    ---------
battery     float
contact     boolean
current     float
...
But after copying this to a testtable, the tags where gone and everything was a field. 

This is not a big problem - you can work with that data without a problem. BUT if you want to copy it back or merge it to the original table, you will get a table with the additional columns host_1 and topic_1.

This is because for influx you already had a column host. So it added a column field host_1. 

If a query in this new table (with host + host_1) spans over a time where both of this columns are in, you only select the data, with the entry host. If the time spans only entries with host_1, it is shown as host and you get your data. Really a unpredictable way to get data.

What is the solution? Easy:

select * into table1 from mqtt_consumer group by host,topic
The "group by" does not group anything. It just tells influx: host & topic are tags and not fields. Please do not transform them...


Nov 26, 2021

Raspberry PI on Ubuntu: yarn: Cannot find module 'worker_threads'

This evening i tried to install a nodejs application with yarn on my raspberry pi. This failed with:

/usr/local/bin/yarn install
internal/modules/cjs/loader.js:638
    throw err;
    ^
Error: Cannot find module 'worker_threads'
    at Function.Module._resolveFilename (internal/modules/cjs/loader.js:636:15)
    at Function.Module._load (internal/modules/cjs/loader.js:562:25)
    at Module.require (internal/modules/cjs/loader.js:692:17)
    at require (internal/modules/cjs/helpers.js:25:18)
    at /opt/zwavejs2mqtt/.yarn/releases/yarn-3.1.0-rc.8.cjs:287:2642
    at Object.<anonymous> (/opt/zwavejs2mqtt/.yarn/releases/yarn-3.1.0-rc.8.cjs:585:7786)
    at Module._compile (internal/modules/cjs/loader.js:778:30)
    at Object.Module._extensions..js (internal/modules/cjs/loader.js:789:10)
    at Module.load (internal/modules/cjs/loader.js:653:32)
    at tryModuleLoad (internal/modules/cjs/loader.js:593:12)

This error occurs because the nodejs version which is delivered by ubuntu is version v.10.19.0.

You have to download the armv8 package from https://nodejs.org/en/download/

With version v16.13.0 the error was gone...

 

Nov 20, 2021

AZ-900 achieved: Microsoft Azure Fundamentals

Yesterday evening i passed Microsofts AZ-900 exam:

Taking the exam on site was no option because of COVID-19, so tried the first time the online option. Nice thing: Many schedules and i chose 20:45. 

As examinee you have to start your online session half an hour earlier and this time you really need for the onboarding: 

  1. Download the software to your PC and do some checks (audio, network, ...)
    This is an .exe - so only windows PCs are possible
  2. Install the app "Pearson VUE" on your smartphone to provide
    1. selfie
    2. passport/driver license/...
    3. photos of your room
  3. Talking to an instructor
    You are not allowed to wear a headset - even a watch is not allowed

 After that the exam is about 40 questions in 45 minutes - quite fair.

 The questions are about these topics:

  • Describe cloud concepts (20-25%)
  • Describe core Azure services (15-20%)
  • Describe core solutions and management tools on Azure (10-15%)
  • Describe general security and network security features (10-15%)
  • Describe identity, governance, privacy, and compliance features (15-20%)
  • Describe Azure cost management and Service Level Agreements (10-15%)

More information can be found here: https://query.prod.cms.rt.microsoft.com/cms/api/am/binary/RE3VwUY

If you want to do this exam, start here: