Raspberry Pi / Linux Cheat Sheet

I’m putting things here I often come back to with Raspberry Pi Setups but didn’t think they’d actually belong in their own article, at least as of yet.

Detecting SSH vs console

I’ve used this when wanting to start certain code when in console mode vs SSH logins. Edit ~/.profile and add commands as needed.

if [ "$SSH_CONNECTION" != "" ]; then
  echo SSH being used, enabling ssh-session specific functionality
else
  echo Enabling console-specific functionality
fi

Shell Scripting

Trapping program execution time in a wrapper shell script

I used this to time C64 demos when I was curating lists for my stream. I would play a demo until I was finished or it was over and when I would exit VICE the elapsed time would print out. First time I ever had to trap in a shell script.

#!/bin/bash

function ctrl_c() {
    echo "** Trapped CTRL-C"
}

trap ctrl_c INT

start_time="$(date -u +%s)"
/home/pi/viceinstall/bin/x64 -autostart ./$1 > executionlog.txt
end_time="$(date -u +%s)"
echo "time elapsed: $(($end_time-$start_time))"

Networking

apt update/install/upgrade fails with ipV6 lookup

From Stack Overflow – ‘Just to get it to work’

Add -o Acquire::ForceIPv4=true when running apt-get.

If you want to make the setting persistent just create /etc/apt/apt.conf.d/99force-ipv4 and put Acquire::ForceIPv4 "true"; in it:

echo 'Acquire::ForceIPv4 "true";' | sudo tee /etc/apt/apt.conf.d/99force-ipv4