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Raspberry Pi related information

You want to minimize the write access to the SD card. This kiosk and its DB should live on NFS (or another network mount).

Automatic startup

We created a custom user (kaffee-user in this example).

X server startup file /etc/X11/Xsession.d/96kaffee-tmux:

sudo -u kaffee-user bash /kaffee/start-tmux.sh &

I have this file /kaffee/start-tmux.sh:

#!/bin/bash

set -x

tmux new-session -d -s kaffee
tmux send-keys /kaffee/start-kiosk.sh C-m

And this file /kaffee/start-kiosk.sh:

#!/bin/bash

set -x

export DISPLAY=:0
# XAUTHORITY not necessarily needed with xhost, see below.
# export XAUTHORITY=/home/pi/.Xauthority
cd /kaffee/kiosk

while true; do
  python3 ./main.py --db ../db
  sleep 5
done

This assumes that pi is the main user which automatically logs in to the graphical desktop. For the user pi, it is probably necessary to give permission for the X access. For a newer Debian 12.5, we did that via /home/pi/.config/wayland.ini:

[autostart]
xauth_coffee = $HOME/bin/auth_coffee.sh

And /home/pi/bin/auth_coffee.sh:

#!/bin/bash
sleep 10  # make sure X is available
xhost +local:kaffee-user  # give permission

Logging

Either the log files should go also on the NFS, or you want to disable them. Edit ~/.kivy/config.ini:

[kivy]
...
log_enable = 0

Touchscreen

I needed to change ~/.kivy/config.ini to allow the touchscreen input:

[input]
mouse = mouse
%(name)s = probesysfs,provider=hidinput
# https://github.com/kivy/kivy/issues/3640
# mtdev_%(name)s = probesysfs,provider=mtdev  # try enabling on older Pis?
hid_%(name)s = probesysfs,provider=hidinput

[modules]
touchring =

To rotate the touchscreen, probably the easy solution is to add this to ~/.kivy/config.ini:

[graphics]
...
rotation = 270

Another alternative option to do it for the whole system, which however does not fully work yet:

I modified /boot/config.txt to rotate our touchscreen:

# https://elinux.org/RPiconfig
# default is 64
gpu_mem=128
# 90 degrees
display_rotate=1

I created a new file /etc/X11/Xsession.d/90rotatetouch to also rotate the input:

# https://wiki.ubuntu.com/X/InputCoordinateTransformation
xinput set-prop "ELAN Touchscreen" "Coordinate Transformation Matrix" 0 1 0 -1 0 1 0 0 1

However, mtdev seems to ignore this. Probably there is a way to also tell mtdev to rotate, but I don't know how, and I just use the other option via the Kivy option now.

ntpdate

It seems that the local clock/time is not so good/accurate. Running sudo ntpdate-debian frequently will fix this. You might need to edit /etc/default/ntpdate. Or it actually seems to use systemd-timesyncd, thus edit /etc/systemd/timesyncd.conf. In our case, the default NTP servers (0.debian.pool.ntp.org etc) did not seem to work, and we had to use services-0.informatik.rwth-aachen.de instead.

Remote admin access

For the tool remote-admin.py:

It seems that /etc/hosts has a weird entry for the hostname (127.0.1.1). The IPython/Jupyter server will bind to this IP, and thus not be accessible from the network. Just remove this entry from /etc/hosts. Then it should bind to the correct ethernet IP for the hostname.

Shell environment

We need UTF8 encoding support in the terminal. Edit /etc/locale.gen and uncomment the line with en_US.UTF-8. Then run sudo locale-gen and sudo update-locale LANG=en_US.UTF-8. Reboot. Check that locale now shows en_US.UTF-8.

Stability

The kiosk software runs fine for 1-2 weeks or so but then becomes laggish. Probably there is some resource leakage, by our kiosk, by Kivy, or by any of the used libraries. This is hard to debug, and also hard to fix (esp if not in our code), so as a simple work around, we installed an automatic restart of the kiosk software during the night (see kill_at_night in the code).

The Pi itself ran fine for about 3 months, after which we also hit probably some OOM (it mostly froze; we had to hard restart).