This program controls the fan on my Raspberry Pi 4 when it gets hot.
Cross build for rpi4:
cross build --release --target aarch64-unknown-linux-musl --verbose
# copy over:
scp target/aarch64-unknown-linux-musl/release/raspberrypi-gpio root@x.x.x.x:/tmp/
Run it (ref: https://stackoverflow.com/questions/27634696/how-to-run-a-script-in-background-linux-openwrt )
(/tmp/raspberrypi-gpio >/dev/null 2>&1 )&