GPIO Hardware Permissions

Interfacing with hardware devices—such as dew heaters, cooling fans, stepper focusers, and relay switches—requires read and write access to GPIO character devices (/dev/gpiochip*). On many single-board computers (Raspberry Pi, Orange Pi, Rockchip, and Armbian-supported platforms), access is restricted to the root user by default.

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1. Group Membership

Ensure the service user executing indi-allsky belongs to the appropriate device groups:

sudo usermod -aG dialout,gpio indi-allsky

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2. Udev Rule Configuration

To grant persistent non-root read/write permissions across reboots, install a udev rule targeting the modern gpiochip character device subsystem:

sudo tee /etc/udev/rules.d/99-gpio.rules <<'EOF'
# Modern Linux gpiochip subsystem
SUBSYSTEM=="gpio", KERNEL=="gpiochip*", GROUP="dialout", MODE="0660", TAG+="uaccess"

# Legacy sysfs GPIO interface (if applicable)
SUBSYSTEM=="gpio", KERNEL=="gpio*", ACTION=="add", PROGRAM="/bin/sh -c 'chown -R root:dialout /sys/class/gpio && chmod -R 770 /sys/class/gpio'"
EOF

Apply the udev rules immediately without rebooting:

sudo udevadm control --reload-rules
sudo udevadm trigger --subsystem-match=gpio

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3. Verification

Verify that the GPIO device nodes reflect the correct group permissions (dialout or gpio with read/write access):

ls -l /dev/gpiochip*

Expected output format:

crw-rw---- 1 root dialout 254, 0 Oct 16 12:00 /dev/gpiochip0
crw-rw---- 1 root dialout 254, 1 Oct 16 12:00 /dev/gpiochip1

If libgpiod-utils is installed, enumerate detected GPIO chips and pin availability:

gpiodetect
gpioinfo