Igor Kromin |   Consultant. Coder. Blogger. Tinkerer. Gamer.

I went to the trouble of making an external power button for my Odroid XU4 and then found out that out of the box DietPi completely ignores this button being pressed. Luckily there is a way to make the OS shut down after the power button is pressed.

Here's what I did to check if the power button presses do anything. I needed to install evtest first.
apt-get install evtest

After it was installed, I ran it and got the following output:
No device specified, trying to scan all of /dev/input/event*
Available devices:
/dev/input/event0: gpio_keys.7
/dev/input/event1: ADS7846 Touchscreen
/dev/input/event2: UVC Camera (046d:0825)

Selecting '0' gave me this...
Input driver version is 1.0.1
Input device ID: bus 0x19 vendor 0x1 product 0x1 version 0x100
Input device name: "gpio_keys.7"
Supported events:
Event type 0 (EV_SYN)
Event type 1 (EV_KEY)
Event code 116 (KEY_POWER)
Testing ... (interrupt to exit)

...and when I triggered the power button, a bunch of events were fired, so I was on the right track!
Event: time 1474075323.624805, type 1 (EV_KEY), code 116 (KEY_POWER), value 1
Event: time 1474075323.624805, -------------- EV_SYN ------------
Event: time 1474075323.829555, type 1 (EV_KEY), code 116 (KEY_POWER), value 0
Event: time 1474075323.829555, -------------- EV_SYN ------------

I came across this forum post that gave me some good leads, but it wasn't for an XU4, so using the default systemd power switch rules I came up with something that should work on the XU4...
ACTION=="remove", GOTO="power_switch_end"
SUBSYSTEM=="input", KERNEL=="event*", SUBSYSTEMS=="platform", DRIVERS=="gpio-keys", ATTRS{keys}=="*,116|116,*|116|*,116,*", TAG+="power-switch"

The above was saved to /etc/udev/rules.d/70-power-switch-odroidxu4.rules and then I ran the following commands to reload the rules...
systemctl restart systemd-udevd
udevadm trigger

Then as soon as I triggered the power button, my XU4 started shutting down. Neat!


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