I tried this script and got this output:

root@GL-AR750S:~# ./wan-watchdog.sh
sh: “0”: out of range
./wan-watchdog.sh: line 17: can't create /sys/class/leds/gl-ar750s:white:usbpower/brightness: nonexistent directory
./wan-watchdog.sh: line 19: can't create /sys/class/leds/gl-ar750s:white:usbpower/brightness: nonexistent directory
root@GL-AR750S:~#

Any ideas @alzhao ?