Creating /boot/ssh and /boot/wpa_supplicant.conf (for a headless setup) works, but how?

[RichardBronosky]

Have you ever wondered HOW this works? I did. And it was quite the rabbit hole to go down.

• First I Googled and found the documentation about creating the file /boot/ssh
• I never managed to find any official documentation on creating the file /boot/wpa_supplicant.conf (Though I did find lots of references that stated that it did work.)
• Then I studied https://github.com/RPi-Distro/pi-gen extensively.
• But I couldn't find anything that looked for /boot/ssh or /boot/wpa_supplicant.conf
• Then I started looking for packages that may contain the implementation.

  Code: Select all

  ~/src/pi-gen $ cat $(find stage[012] -type f -name '*package*') | tr " " "\n" | grep 'pi' | sort
  libraspberrypi-bin
  libraspberrypi-dev
  libraspberrypi-doc
  libraspberrypi0
  pi-bluetooth
  python-rpi.gpio
  raspberrypi-bootloader
  raspberrypi-net-mods
  raspberrypi-sys-mods
  raspi-config
  raspi-copies-and-fills
  rpi-update
  

• I grabbed all the matching packages I could find in https://archive.raspberrypi.org/debian/pool/main/r/
• I got lucky with raspberrypi-net-mods and raspberrypi-sys-mods

I finally discovered that it is a bit of systemd magic that makes each happen.

raspberrypi-net-mods.service

Code: Select all

[Unit]
Description=Copy user wpa_supplicant.conf
ConditionPathExists=/boot/wpa_supplicant.conf
Before=dhcpcd.service

[Service]
Type=oneshot
RemainAfterExit=yes
ExecStart=/bin/mv /boot/wpa_supplicant.conf /etc/wpa_supplicant/wpa_supplicant.conf
ExecStartPost=/bin/chmod 600 /etc/wpa_supplicant/wpa_supplicant.conf

[Install]
WantedBy=multi-user.target

Notice the ConditionPathExists and ExecStart! That's pretty clever.

Similarly, but slightly more clever.

raspberrypi-sys-mods.sshswitch.service

Code: Select all

[Unit]
Description=Turn on SSH if /boot/ssh is present
ConditionPathExistsGlob=/boot/ssh{,.txt}
After=regenerate_ssh_host_keys.service

[Service]
Type=oneshot
ExecStart=/bin/sh -c "update-rc.d ssh enable && invoke-rc.d ssh start && rm -f /boot/ssh ; rm -f /boot/ssh.txt"

[Install]
WantedBy=multi-user.target

Now that I've uncovered this, I can finally finish the project I started with this thread nearly 5 years ago. It's been a long journey of discovery, this $35 whim I indulged in back in May 2012

[gibatronic]

Nowadays they have this tiny guide: Setting up a Raspberry Pi headless

[RichardBronosky]

That simply states that it works. It doesn't tell you how/why. My post is about the technical implementation.

[DougieLawson]

That simply states that it works. It doesn't tell you how/why. My post is about the technical implementation.

You can create both of those on Windows with Notepad++.

/boot/ssh can be an empty file.
/boot/wpa_supplicant.conf needs to look like

Code: Select all

country=GB
ctrl_interface=DIR=/var/run/wpa_supplicant GROUP=netdev
update_config=1
network={
        ssid="your WiFi SSID goes here"
        psk="your WiFi password goes here"
}

Note: change the country=?? line to have your ISO 2-char country code.

[snaiperis]

You can create both of those on Windows with Notepad++.

This doesn't help to understand, how it works.

Thanks, Richard, this was what I was looking for.

[Seeking Sooth]

Richard, I completely get your quest and appreciate it!

Clever and Elegant.

Thanks.