magic_shutdown: Shutdown computer remotely using Magic Packet

The title says it all. If you don’t know what a Magic Packet is then read here. Below is the code of a shell script (I call magic_shutdown) that uses tcpdump to listen for Magic Packets. When it receives on then the shell script verifies its content to make sure that this packet was meant for this computer. Note this script doesn’t require that your network interface card support Wake-on-LAN. It has no special hardware dependencies.

All-in-all, this script lets you create create a shortcut which will act as remote power button for your computer. Press it to turn the computer ON. Press it again to turn the computer OFF.

Get magic_shutdown‘s code
License: GNU Public License version 3.

#!/bin/bash
#Author:AppleGrew
#License:GPL version 3

listenPort=9
interface="eth0"

#Forking to daemonize...
if [[ "$2" != "forked" ]]
then
 echo "Forking $0..."
 "$0" "$1" forked &
 echo "Forked."
 exit 0
fi

#Creating pid file
ppid=$$
echo $ppid >"$1"

echo "Started"
mac=`ifconfig "$interface"|head -n1|sed  -e 's/.*HWaddr \([0-9:a-fA-F]*\)/\1/g' -e 's/://g'`
pckt_expect=`echo "ff ff ff ff ff ff $mac $mac $mac $mac $mac $mac $mac $mac"|sed 's/ //g'|tr 'A-Z' 'a-z'`
while `true`
do
 pckt_data=`tcpdump -i "$interface" -x -c 1 udp port ${listenPort}`
 if [[ $? != 0 ]]
 then
  echo "tcpdump returned error."
  exit 1
 fi
 
 pckt_data=`echo "$pckt_data" | \
  grep '0x[0-9]*:'| \
  tr 'A-Z' 'a-z'| \
  sed 's/[ \t]//g'| \
  sed 's/0x[0-9]*:\([0-9a-f]*\)/\1/g'| \
  tr -d '\n\r'| \
  cut -c 57-`
 if [[ "$pckt_data" == "$pckt_expect" ]]
 then
  echo "Matched! Received Magic packet shutting down..."
  shutdown -P now #Not recommended
  #For Gnome #Doesn't work dunno why?
  #dbus-send --session --dest=org.gnome.PowerManager \
  # --type=method_call --print-reply --reply-timeout=2000 \
  # /org/gnome/PowerManager org.gnome.PowerManager.Shutdown
  #For KDE 3.5
  #dcop `dcop|grep power-manager` power-manager shutdown
  exit 0
 fi
done

echo "EXITED"
exit 0

Below is the startup script that must be used to launch magic_shutdown script.

Get launch_magic_shutdown‘s code
License: GNU Public License version 3.

#!/bin/bash
#Author:AppleGrew
#License:GPL version 3

SCRIPT="/opt/magic_shutdown"
PID_FILE="/var/run/magic_shutdown.pid"
case "$1" in
 start)
 test -f "$PID_FILE" && echo "Already Running..." && exit 1
 "$SCRIPT" "$PID_FILE"
 echo "Started"
 ;;
 stop)
 pid=`cat "$PID_FILE"`

 tcpPid=`pgrep -P $pid tcpdump`
 kill -9 $pid
 kill -2 $tcpPid
 if [ -f "$PID_FILE" ] && ! ps -p $pid >/dev/null
 then
 rm -f "$PID_FILE"
 else
 echo "Failed to delete pid file. Maybe its already deleted."
 fi
 echo "Stopped"
 ;;
esac

Installations:-
Assuming that you have downloaded the above two codes into your home directory. Now run the following commands.

sudo cp launch_magic_shutdown /etc/init.d
sudo chmod a+x /etc/init.d/launch_magic_shutdown
cd /etc/rc2.d
sudo ln -s ../init.d/launch_magic_shutdown S99launch_magic_shutdown

sudo cp magic_shutdown /opt/magic_shutdown
sudo chmod a+x /opt/magic_shutdown

Hope this helps. Report in the comments section if you encounter any problem.


Update: Stuart’s Script
Stuart (see comment section) posted his version of magic_shutdown script. If the above one doesn’t work then maybe you should give this one a try.

#!/bin/sh
#Author: Stuart
#Original Author:AppleGrew
#License:GPL version 3

#Forking to daemonize...
if [[ "$2" != "forked" ]]
then
 echo "Forking $0..."
 "$0" "$1" forked &
 echo "Forked."
 exit 0
fi

#Creating pid file
ppid=$$
echo $ppid >"$1"

echo "Started"
interface=`route -n | grep "^0.0.0.0" | awk -F " " '{print $8}'`
mac=`ifconfig "$interface"|head -n1|sed  -e 's/.*HWaddr \([0-9:a-fA-F]*\)/\1/g' -e 's/://g'`
pckt_expect=`echo "$mac $mac $mac $mac $mac $mac $mac $mac $mac $mac $mac $mac $mac $mac $mac $mac"|sed 's/ //g'|tr 'A-Z' 'a-z'`
while `true`
do
 pckt_data=`tcpdump -i "$interface" -s 0 -x -c 1 \( \(ether dst "$mac" and not ip and not arp and not rarp\) or \(udp port 9\) \)`
 if [[ $? != 0 ]]
 then
 echo "tcpdump returned error."
 exit 1
 fi
 pckt_data=`echo "$pckt_data" | \
 grep '0x[0-9]*:'| \
 tr 'A-Z' 'a-z'| \
 sed 's/[ \t]//g'| \
 sed 's/0x[0-9]*:\([0-9a-f]*\)/\1/g'| \
 tr -d '\n\r' | \
 awk -F "ffffffffffff" '{print $2}'`
 if [[ "$pckt_data" == "$pckt_expect" ]]
 then
 echo "Matched! Received Magic packet shutting down..."
 rm -f $1
 /sbin/poweroff
 exit 0
 fi
done

echo "EXITED"
exit 0
Comments
3 Responses to “magic_shutdown: Shutdown computer remotely using Magic Packet”
  1. Alex says:

    And tool for lazy – Wake-On-LAN over Internet with scheduling – http://www.rshut.com/wol

  2. Stuart says:

    Hi,
    Just what I was looking for :O) saved me some work, but I did find I needed to make some changes. The tcpdump filter wouldn’t work for magic packet sent over ethernet only, i.e. not UDP, so I changed the filter to capture both. Also The parsing didn’t work as it seems the MAC address is not repeated 16 times. Lastly, the “ps -p” didn’t work on my platform, so I made a more portable version checking for the PID. Attached is the updated script if you want it.

    I forgot, I also changed the packet parsing to break the packet up using the ffffffffffff in the packet as the two types of packet are of differnt lengths if using UDP or not, and also added a statement to determine the “main” ethernet interface of the machine so it would automatically work for devices other than eth0.

    Thanks again…
    Stuart/

    #!/bin/sh
    #Original Author:AppleGrew
    #License:GPL version 3

    #Forking to daemonize…
    if [[ “$2” != “forked” ]]
    then
    echo “Forking $0…”
    “$0” “$1” forked &
    echo “Forked.”
    exit 0
    fi

    #Creating pid file
    ppid=$$
    echo $ppid >”$1″

    echo “Started”
    interface=`route -n | grep “^0.0.0.0″ | awk -F ” ” ‘{print $8}’`
    mac=`ifconfig “$interface”|head -n1|sed -e ‘s/.*HWaddr \([0-9:a-fA-F]*\)/\1/g’ -e ‘s/://g’`
    pckt_expect=`echo “$mac $mac $mac $mac $mac $mac $mac $mac $mac $mac $mac $mac $mac $mac $mac $mac”|sed ‘s/ //g’|tr ‘A-Z’ ‘a-z’`
    while `true`
    do
    pckt_data=`tcpdump -i “$interface” -s 0 -x -c 1 \( \(ether dst “$mac” and not ip and not arp and not rarp\) or \(udp port 9\) \)`
    if [[ $? != 0 ]]
    then
    echo “tcpdump returned error.”
    exit 1
    fi
    pckt_data=`echo “$pckt_data” | \
    grep ‘0x[0-9]*:’| \
    tr ‘A-Z’ ‘a-z’| \
    sed ‘s/[ \t]//g’| \
    sed ‘s/0x[0-9]*:\([0-9a-f]*\)/\1/g’| \
    tr -d ‘\n\r’ | \
    awk -F “ffffffffffff” ‘{print $2}’`
    if [[ “$pckt_data” == “$pckt_expect” ]]
    then
    echo “Matched! Received Magic packet shutting down…”
    rm -f $1
    /sbin/poweroff
    exit 0
    fi
    done

    echo “EXITED”
    exit 0

  3. Apple Grew says:

    That’s great Stuart. I have added your code to my post.

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