#!/bin/sh
A=/sys/class/dmi/id/product_serial
B=/ofw/mfg-data/SN
C=/proc/device-tree/mfg-data/SN
if [ -e $A ]; then
    read value < $A
    echo "$value"
elif [ -e $B ]; then
    read value < $B
    echo "$value"
elif [ -e $C ]; then
    read value < $C
    echo "$value"
else
    echo unknown
fi
