Raspberry Pi / Linux Cheat Sheet

Last Updated on May 28, 2023.

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.

Auto mount USB stick

See https://krystof.io/auto-mounting-a-usb-drive-in-a-raspberry-pi/

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))"

Another example that traps the exiting of a shell (since we set -e to turn on exit on error)

set -e
trap 'catch $? $LINENO' EXIT
catch() {
  echo "catching!"
  if [ "$1" != "0" ]; then
    # error handling goes here
    echo "Error $1 occurred on $2"
  fi
}

Redirecting Nohup

Nohup redirects output and is often used for running programs in the background. If I don’t want the nohup.out and just want to redirect to null, I can do this:

nohup command </dev/null >/dev/null 2>&1 &

Reference: https://stackoverflow.com/questions/10408816/how-do-i-use-the-nohup-command-without-getting-nohup-out

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

Ubuntu Wifi / Network Setup with netplan

I use these when I’m using Ubuntu server and need to get Wifi working.

List Network Devices – Wifi is generally wlXXXXXX

ls /sys/class/net

Edit the netplan config file (Ubuntu server was at /etc/netplan/00-installer-config.yaml, and reworked accordingly. Sample:

network:
    ethernets:
        eth0:
            dhcp4: true
            optional: true
    version: 2
    wifis:
        wlp3s0:
            optional: true
            access-points:
                "SSID-NAME-HERE":
                    password: "PASSWORD-HERE"
            dhcp4: true

Follow with sudo netplan apply to finish up.

Peripheral Devices

Mouse Polling Rate

I used this to boost mouse polling rate when using a Raspberry Pi as a modern day Steamlink (since Steamlink is discontinued and who knows how long mine will live) using Parsec/Moonlight.

Add this to the end of /boot/cmdline.txt:

usbhid.mousepoll=8

The lower you go the more CPU the Pi will use for this.

Reference: https://support.parsecgaming.com/hc/en-us/articles/115002699012-Setting-Up-On-Raspberry-Pi-Raspbian-

System Versions and Firmware

Check Firmware Version

sudo /opt/vc/bin/vcgencmd version

Update firmware – check version:

sudo rpi-eeprom-update

Update via normal update with full-upgrade switch:

sudo apt update
sudo apt full-upgrade

To ONLY update firmware:

sudo rpi-eeprom-update -d -a

Network Backup

This is a nice setup that I’ve used to take occasional snapshots of Raspberry Pi computers I’ve setup for internal network components. I generally shut down any docker or webmin services before running it.

Network Backup your Raspberry Pi

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