Script to automatically bind and unbind external USB drive on Synology NAS

bind-backup.sh

#!/bin/bash

SERIAL="00000000"

echo "Looking for device with serial $SERIAL..."
for d in /sys/bus/usb/devices/*-*; do
    if [[ -f "$d/serial" ]]; then
        serial=$(<"$d/serial")
        if [[ "$serial" = "$SERIAL" ]]; then
            device="$(basename $d)"
            break
        fi
    fi
done

if [[ -z "$device" ]]; then
    echo "Fail to find device with serial $SERIAL"
    exit 1
fi

echo "Binding device $device..."
echo "$device" > /sys/bus/usb/drivers/usb/bind || exit 1

echo -n "Waiting for filesystem to mount... "
exec 3< <(tail -f -n1 /var/log/kern.log)
while read line; do
    if [[ "$line" = *"[EXFAT] mounted successfully" ]]; then
        echo "Mounted!"
        break
    elif [[ "$line" = *"usb $device: "* && "$line" = *" error "* ]]; then
        echo "Error!"
        exit 1
    fi
done <&3

echo -n "Waiting for filesystem to unmount... "
while read line; do
    if [[ "$line" = *"[EXFAT] unmounted successfully" ]]; then
        echo "Unmounted!"
        break;
    fi
done <&3

echo "Unbinding device $device..."
echo "$device" > /sys/bus/usb/drivers/usb/unbind

The script here relies on the log from kernel, and it apparently supports only exFAT filesystem. I have no idea about your system and external disk so I can't really provide any advice. There is probably a better way to detect mounting and unmounting... but as it's working for me, I'm not very motivated to investigate further.

Also, don't you need to put
exec 3< <(tail -f -n1 /var/log/kern.log)
in front of

no, actually that would probably be wrong, IIRC. The previous one would be reused by the second loop.