Wake-on-LAN

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Introduction

This article deals with Wake-on-LAN (wol, wake on lan), what it is, how it can be used from an Arch Linux computer, and its general uses. Basically put, Wake-on-LAN, otherwise known as 'wol' is the ability to switch a computer that is connected to a network (be it the internet or intranet) on. This can be a very useful ability.

It is important to note that Wake-on-LAN applies to the computers being physically connected (ie, not wireless).

Does my motherboard support Wake-on-LAN?

For Wake-on-LAN to work, the target computer motherboard must support this feature. Generally speaking, the Wake-on-LAN (non)ability of the target motherboard will be specified by the hardware manufacturer. Sometimes, this ability is evident by browsing through said motherboard's BIOS and looking for something like 'PCI Power up'. Most modern motherboards should support Wake-on-LAN.

Ensure that Wake-on-LAN is enabled and survives a reboot

A common problem with the Wake-on-LAN in computers running Linux is that the network drivers have Wake-on-LAN switched off by default. To manually switch on the Wake-on-LAN feature on your driver, you'll need ethtool:

pacman -Sy ethtool

First query the driver to see if it's defaulted to 'on' by using ethtool:

 ethtool eth0 | grep Wake-on
        Supports Wake-on: pg
	Wake-on: d
Note: We need a 'Wake-on' value of 'g' for WOL to work.

To enable the wol feature in the driver, simply run the following

ethtool -s eth0 wol g

This command does not last beyond the next reboot. To execute the command every time you shutdown your computer, add the command using an absolute path into Template:Filename using your fav text editor.

Note: I placed the following lines BEFORE the "# Terminate all processes" but I don't think it really matters.
# Setup WOL for next boot
stat_busy "Setting WOL to Active"
/usr/sbin/ethtool -s eth0 wol g
stat_done

For more information on this, please read the wol FAQ (not available at the moment - 11/12/2008)

  • If for some reason, you find that after using the command to switch your network drivers Wake-on-LAN feature on, the computer shuts down normally but then starts again, experiment with combinations of [u/b/m]g

Wake-on-LAN in different situations

The computer that you want to use Wake-on-LAN on may be directly linked to your computer through a network cable, connected to the same router that you are using, or remotely, across the internet.

There are four essential things needed in order to use Wake-on-LAN on a target PC:

  1. Some kind of Wake-on-LAN software on the host (your) PC
  2. A connection to the internet or intranet of the target PC
  3. The MAC address of the target PC
  4. The internal or external IP of the target PC
  • Firstly, install a Wake-on-LAN software. In this article, wol will be used. It can be installed from the [community] repository.
  • It is recommended that you read the documentation of wol
man wol
wol --help
  • wol requires several parameters, the most basic needed:
wol MACADDRESS
  • But it is good practice to include the IP address or hostname, therefore this syntax should be the minimal used:
wol -i HOSTNAME_OR_IP MACADDRESS
  • The documentation of wol states that:
Each MAC-ADDRESS is written as x:x:x:x:x:x, where x is a hexadecimal number between 0 and ff which represents one byte of the address, which is in network byte order (big endian).
  • To obtain the MACADDRESS of the target computer:
ifconfig | grep HWaddr

The port, IP or hostname of the target PC will be addressed in the relevant following sections.

Across your intranet/network (no router)

If you are connected directly to another computer through a network cable, or have disabled your router firewall (not a good idea), then using Wake-on-LAN should be very simple.

For two computers connected to each other

wol MACADDRESS_OF_TARGET_PC

For computers connected to a non-firewalled router

wol -i INTERNAL_IP_OF_TARGET_PC MACADDRESS_OF_TARGET_PC
  • To find the internal IP (it's the first grepped entry):
ifconfig | grep 'inet addr'
  • Since you are not firewalled, then there is no need to worry about port redirects.
  • If you intend to continue using Wake-on-LAN, it is recommended that you assign your computer's MACADDRESS to a specific IP on your router. Consult your router for details as to how to do this.

Across your intranet/network (router)

The syntax used in this situation:

wol -p PORT_FORWARDED_TO_INTERNAL_IP -i INTERNAL_IP MACADDRESS_OF_TARGET_PC
  • When you send the MagicPacket signal to the target computer via a specific port, the signal passes through your router. The router must be instructed to forward any signal heading for that specific port to the internal IP of the target PC.
  • It is recommended that for multiple computers connected to one computer, to assign a different port forward to each internal IP
  • For port forwarding help, please consult http://portforward.com/ (though this website has some Windows specific content, it has a very large database of router web interfaces)

Across the internet

The syntax needed in this case:

wol -p X -i HOSTNAME_OR_EXTERNAL_IP_OF_TARGET MACADDRESS
  • Assuming that you know the external IP of the target machine, and that the router ports on both sides have been forwarding correctly, then this should be exactly as the syntax states.

Additional Notes

  • A common problem is that some forget to switch on the Wake-on-LAN feature in their BIOS.
  • In some systems the BIOS option "Boot from PCI/PCI-E" needs to be Enabled.

Example WOL script

Here is a script you can use to automate wol to several different machine. Modify as you see fit:

#!/bin/bash

# definition of MAC addresses
monster=01:12:46:82:ab:4f
chronic=00:3a:53:21:bc:30
powerless=1a:32:41:02:29:92
ghost=01:1a:d2:56:6b:e6

while [ "$input1" != quit ]; do
echo "Which PC to wake?"
echo "p) powerless"
echo "m) monster"
echo "c) chronic"
echo "g) ghost"
echo "b) wake monster, wait 40sec, then wake chronic"
echo "q) quit and take no action"
read input1
  if [ $input1 == p ]; then
  /usr/bin/wol $powerless
  exit 1
fi

if [ $input1 == m ]; then
  /usr/bin/wol $monster
  exit 1
fi

if [ $input1 == c ]; then
  /usr/bin/wol $chronic
  exit 1
fi

# this line requires an IP address in /etc/hosts for ghost
# and should use wol over the internet provided that port 9
# is forwarded to ghost on ghost's router

if [ $input1 == g ]; then
  /usr/bin/wol -v -h -p 9 ghost $ghost
  exit 1
fi

if [ $input1 == b ]; then
  /usr/bin/wol $monster
  echo "monster sent, now waiting for 40sec then waking chronic"
  sleep 40
  /usr/bin/wol $chronic
  exit 1
fi

if [ $input1 == Q ] || [ $input1 == q ]; then
echo "later!"
exit 1
fi

done
echo  "this is the (quit) end!! c-ya!"