Mark a Screenshot on Linux

More that than often to explain things quickly, I like to take a screenshot of the (web) application I am talking about, and then circle the corresponding area so that everything is clear. Possibly with a rounded rectangle, as I find it the cutest variant.

This is how I do it on Linux:
Install necessary tools:

apt install gimp scrot                                                                   

Take the screenshot:

# Interactively select a window or rectangle with the mouse                              
scrot --selection screenshot.png                                                                    

Open the screenshot and annotate it with gimp:

gimp screenshot.png                                                                      

Then in gimp:

• Tools -> Selection Tools -> Rectangle Select, and mark the area
• Select -> Rounded Rectangle, and keep the default
• Change the color to a nice blue shade in the toolbox
• Edit -> Stroke selection

Maybe gimp is a bit overkill for that. But instead of learning a limited tool, I prefer to learn an advanced one like gimp step by step.

Opensource Retrocomputing: FreeMiNT on Atari ST

If you have an Atari ST sleeping in the attic, and have an interest for open source Unix, you might be interested to try out ST Mint, a distribution of the FreeMiNT kernel tailored for this platform.

When preparing the last ST Mint release, I noticed that bash needed too much memory for the ST, so I included the sash shell, cross-compiled from the Debian source package.
Funnily enough, although the Atari hardware is physically large and heavy, working on ST Mint feels like doing embedded hardware development: you cross-compile, link with the smallest possible libc, copy stuff on a SD Card, and try to fit everything in 4MB of RAM.

Debian 9 -> 10 Ugrade report

I upgraded my laptop and VPS to Debian 10, as usual in Debian everything worked out of the box, the necessary daemons restarted without problems.
I followed my usual upgrade approach, which involves upgrading a backup of the root FS of the server in a container, to test the upgrade path, followed by a config file merge.

I had one major problem, though, connecting to my php based Dokuwiki subsole.org website, which displayed a rather unwelcoming screen after the upgrade:

I was a bit unsure at first, as I thought I would need to fight my way through the nine different config files of the dokuwiki debian package in /etc/dokuwiki

However the issue was not so complicated: as  the apache2 php module was disabled, apache2 was outputting the source code of dokuwiki instead of executing it. As you see, I don't php that often.

A simple
a2enmod php7.3
systemctl restart apache2

fixed the issue.

I understood the problem after noticing that a simple phpinfo() would not get executed by the server.

I would have expected the upgrade to automatically enable the new php7.3 module, since the oldstable php7.0 apache module was removed as part of the upgrade, but I am not sure what the Debian policy would recommend here, or if I am missing something else.
If I can reproduce the issue in a upgrade scenario, I'll probably submit a bug to the php package maintainers.

PowerShell on Debian

I heard some time ago that Microsoft released their interactive and
scripting language PowerShell under an opensource license (MIT) but I completely missed that they were providing a repository and ready to use packages for your favorite distribution.

Anyway an apt-get away and that's it:



New-Object net.sockets.tcpclient("libera.cc", 80) opens a TCP connection to a target host, a quick way to test if a port is open ( look for Connected: True for a successful socket creation)

Splitting a large mp3 / flac / ogg by detecting silence gaps

If you have a large audio file coming for instance from a whole music album, the excellent mp3splt can do this for you:

mp3splt -o @n-@f -s my_long_file.mp3

will autodetect the silences, and create a list of tracks based on the large file.

mp3splt is  available in the Debian / Ubuntu archive.

Normalize a bunch of audio files to the same loudness

I had a bunch of audio files in a directory, each recorded live with different devices, and it proved very ear-painful to hear the audio files in a playlist because of the difference of loudness.
To normalize audio filesm  you can find a number of tool working with ID3 tags, but after testing with vlc, mplayer, and the pogo mp3 player none of them did produce a measurable change. So I converted everything to wav, normalized the wav files, then converted back to mp3.

delete funny chars and spaces in file names
detox music_dir
converting files to wav is just a matter of
# this uses zsh recursive globbing
for file in **/*.mp3 ; do ffmpeg -i $file  "$(basename $file .mp3).wav"; done
normalizing files with the normalize-audio program, from the debian package of the same name.
# this uses zsh recursive globbing
normalize-audio **/*.wav
converting back to mp3
for file in **/*.wav ; do ffmpeg -b:a 192k -acodec libmp3lame -i $file "$(basename $file .wav).mp3"; done

Test if your microphone input is working from the command line on Linux

arecord -vv /dev/null

That's it. Now clap your hand and observe the ascii vumeter.