Hotplug2 script to automatically start minidlna every time the USB disk gets attached and stop minidlna when disk gets detached. Configuration parameters are at the top of script.

30-minidlna

#!/bin/sh

# Hotlug2 script which starts minidlna when USB disk gets attached

# aarmot@gmail.com
# Sharing: GPLv3 or later

# To handle minidlna startup through hotplug you should disable minidlna autostart
#   /etc/init.d/minidlna disable
# and copy current script to /etc/hotplug.d/block/30-minidlna

# Minimum size (in GB) of disk where minidlna database can be mounted
# This check tries to avoid writing temporal data to USB flash drives
MINIDLNA_USE_DISK=100

# Subdirectory for minidlna DB
MINIDLNA_DIR=.minidlna

# If "1" then minidlna database gets rebuilt from scratch after each mount
MINIDLNA_FORCE_REBUILD=1

# If "1" then swap is unmounted after minidlna DB has been rebuilt
MINIDLNA_RELEASE_SWAP=1

# Script works only on devices sda .. sdh
[ -z "$DEVNAME" -o -n "${DEVNAME#sd[a-h]}" ] && exit 0

start_minidlna() {
	local d
	rm -rf /var/run/minidlna
	if [ $(cat /sys/block/$DEVNAME/size) -gt $(($MINIDLNA_USE_DISK*2048000)) ]; then
		d=$(grep ^/dev/$DEVNAME /proc/mounts | head -1 | cut -d ' ' -f 2)
		if [ -n "$d" ]; then
			mkdir -m 0755 -p $d/$MINIDLNA_DIR
			[ "$MINIDLNA_FORCE_REBUILD" = 1 ] && rm -rf $d/$MINIDLNA_DIR/*
			ln -s $d/$MINIDLNA_DIR /var/run/minidlna
			[ -f $d/.swap ] && swapon $d/.swap
		fi
	fi
	rm -f /var/log/minidlna.log
	/etc/init.d/minidlna restart
	if [ "$MINIDLNA_RELEASE_SWAP" = 1 -a $(cat /proc/swaps | wc -l) -gt 1 ]; then
		sleep 120
		while [ $(ps | grep '[m]inidlna' | wc -l) -gt 1 ]; do
			sleep 60
		done
		swapoff -a
	fi
}

stop_minidlna() {
	/etc/init.d/minidlna stop
	rm -rf /var/run/minidlna
	sleep 10
	d=$(grep /dev/$DEVNAME /proc/mounts | cut -d ' ' -f 2)
	[ -n "$d" ] && umount $d
}

L=/tmp/.mntsrv.lock 
case "$ACTION" in
add)
	if ln -s . $L; then (
		sleep 5
		start_minidlna
		rm -f "$L"
		) &
	fi
	;;
remove)
	if ln -s . $L; then (
		stop_minidlna
		sleep 1
		rm -f "$L"
		) &
	fi
	;;
esac