Fixing sound on RetroPie after updating and installing Desktop Environment

I started out by imaging retropie-buster-4.7.1-rpi2_3.img.gz onto an SD card for a Raspberry Pi 3 B. Then I updated the software using the menus in EmulationStation. Then I installed the desktop environment, again with the ES menus. What resulted was audio no longer working in EmulationStation and the console emulators. I did a whole bunch of things to troubleshoot, so I'm not sure what actually made it work.

/boot/config:

hdmi_drive=2
hdmi_force_hotplug=1
hdmi_force_edid_audio=1

Install:

sudo apt install pavucontrol pulseaudio-utils
sudo apt-get install lxplug-volumepulse

In the desktop environment, add Volume Control panel to the menu bar.

In EmulationStation, Audio Card: hw, Audio Device: HDMI.

Troubleshooting

Play audio with Alsa:

sudo aplay /usr/share/sounds/alsa/Front_Center.wav

Speaker test:

speaker-test -D sysdefault -t wav

sed basics

To replace all instances of http://www.youtube in html files to https://www.youtube:

find . -name "*.html" -exec sed -i 's|http://www.youtube|https://www.youtube|g' {} \;

Fix init sequence in Raspberry Pi

If the init sequence gets broken and you can't get to a shell on a Raspberry Pi (I'm using 3 model B), you can boot into recovery mode this way.

• Hit shift when starting up.
• Hit "e" to edit config
• tab over to cmdline.txt
• add to the end of the line
  init=/bin/sh
• hit ok, then Esc to boot...... it will boot you in to a command line
  # mount -n -o remount,rw / (this will remount / so you can make changes)
• now you should be able to edit the init.d config.
• when you reboot again.... hold shift and remove the init=/bin/sh

Source: raspberrypi.stackexchange.com

Verifying OpenSSL certificates

Verifying that a certificate is issued by a CA

How to use OpenSSL on the command line to verify that a certificate was issued by a specific CA, given that CA's certificate:

$ openssl verify -verbose -CAfile cacert.pem  server.crt
server.crt: OK

Verify that a private key matches a certificate

$ openssl x509 -noout -modulus -in server.crt | openssl md5
$ openssl rsa -noout -modulus -in server.key | openssl md5

The resultant hashes should match.

My temporary development environment

Here is how I set up my tools on a computer I'm temporarily using, such as one at the library.

Putty

1. Download putty from www.chiark.greenend.org.uk
2. Putty > Window > Colours > ANSI Blue > Red: 60, Green: 60, Blue: 255
3. Putty > Session > Default Settings > Save
4. Save a new session with the following set:
1. Session > Host Name
2. Connections > Data > Auto-login username.

 Vim

~/.vimrc:

syntax enable
set ic
set expandtab shiftwidth=4 smarttab autoindent

Note: Superseded by Vim for Python, which is more comprehensive.

 Screen

~/.screenrc:

shell -$SHELL
termcapinfo * ti@:te@
startup_message off

Bash

~/.bash_profile

# EDITOR
export EDITOR=vim

Websites

https://www.blogger.com for note taking
https://github.com

Creating paths in Python

Let's say you had this tree:

/home/me/example.com/passenger_wsgi.py
/home/me/example.com/virtualenv

In the Python script, to refer to the directory that is sibling to the script:

os.path.join(os.path.dirname(os.path.abspath(__file__)), 'virtualenv')

Note that this will yield the same result even if the script is a symlink to a file located elsewhere, i.e. __file__ refers to the location of the symlink and not the original file.

Linux date command

To format a date, e.g. for use in a file name:

NAME=$(date +arbitrary_string-%F/%H%M)
echo $NAME

Result:

arbitrary_string-2017-08-18/1300

Blog from the command line

GoogleCL allows you to post to your Blogger blog from the command line. To install:

1. Install Python gdata libraries. This entails downloading, untarring, and sudo python setup.py
2. Install GoogleCL. Same as above.
3. Copy googlecl-0.9.5/build/scripts-2.6/google (version numbers subject to change) to /usr/local/bin or anywhere else in you PATH.

Now you can open a terminal and run a command like:

google blogger post --tags "online, shell" --title "Frist post using GoogleCL" "Can you believe I'm posting this from the command line?"

Or write your post in a text editor, saving it as ~/tmp/post.html, then:

google blogger post --tags "online, shell" --title "Blog from the command line" ~/tmp/post.html