How do I persist GPIO changes across reboots?

[PHLAK]

I have Armbian up and running on a Rock Pi S with a PoE HAT. To enable the audio jack on the PoE HAT I had to run the following commands as mentioned on the official Rock Pi S PoE Hat wiki.
 

# echo 15 > /sys/class/gpio/export 
# echo out > /sys/class/gpio/gpio15/direction
# echo 1 > /sys/class/gpio/gpio15/value

 

Once enabled, the audio works as needed. However, every time the device is rebooted I have to SSH in and run these commands again to re-enable audio out which is obviously not ideal.

 

How can I persist these changes between reboots?

 

[PHLAK]

I was able to solve this by using systemd-tmpfiles to modify these values on boot. Specifically I created a file `/etc/tmpfiles.d/enable-audio-jack.conf` with the following contents.

 

w /sys/class/gpio/export - - - - 15
w /sys/class/gpio/gpio15/direction - - - - out
w /sys/class/gpio/gpio15/value - - - - 1