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Wake On LAN

Some notes on getting the Wake On LAN (WOL) feature to work with a Debian system.


Your first step towards booting your computer from over the network is to make sure your Ethernet card and mother board support some type of Wake On LAN feature. Notably 3Com's -NM (non managed) cards do not support WOL while their -M (managed) cards do.

There are two main systems. The older method uses a Wake On LAN three pin connector between your Ethernet card and your main board. Both headers are usually labelled 'wol'. The newer system uses a Wake On LAN pin on the PCI bus, negating the need for the cable. Some main boards support both and only provide the header for backwards compatibility with Ethernet cards that don't support the PCI pin.

Recent motherboards with onboard NICs support Wake On LAN without the need for any pins/cables.

Firmware / BIOS

In a nice BIOS under power management you will have a clear, intuitive option labeled "Wake On LAN". Unfortunately my system wasn't so clear and has a couple options available. One seems to always work, the other sometimes works. I built upon the information shared by Mark Ivey since I also have a Shuttle XPC SK41G and am using the "PowerOn by PCI Card" option with success.1


Interface setup


add this file

$ cat /etc/network/interfaces.d/eth0
auto eth0
iface eth0 inet dhcp
        ethernet-wol g

reboot. Check if it worked with

$ sudo ethtool eth0

Settings for eth0:
        Supported ports: [ MII ]
        Supported link modes:   10baseT/Half 10baseT/Full 
                                100baseT/Half 100baseT/Full 
        Supported pause frame use: No
        Supports auto-negotiation: Yes
        Advertised link modes:  10baseT/Half 10baseT/Full 
                                100baseT/Half 100baseT/Full 
        Advertised pause frame use: No
        Advertised auto-negotiation: Yes
        Speed: 100Mb/s
        Duplex: Full
        Port: MII
        PHYAD: 1
        Transceiver: external
        Auto-negotiation: on
        Supports Wake-on: g
        Wake-on: g
        Link detected: yes

Wake-on: g means it worked


As of Squeeze ethtool parameters can be set directly from /etc/network/interfaces. The above can be achieved like this:

iface eth0 inet dhcp
        ethernet-wol g

The script /etc/network/if-up.d/ethtool will then take care of calling ethtool on ifup. See /usr/share/doc/ethtool/README.Debian for more information.

You can then power down your system, and prepare the other system to wake it.

Before squeeze

After activating Wake On LAN in hardware it is also necessary to activate it in software. This is done using ethtool, which tells the interface to respond to the magic packet. Replace eth0 with your network interface device name:

$ su
# aptitude install ethtool
# ethtool -s eth0 wol g

This can be automated by editing /etc/network/interfaces:

iface eth0 inet dhcp
        post-up /sbin/ethtool -s $IFACE wol g
        post-down /sbin/ethtool -s $IFACE wol g

This runs ethtool after every time eth0 is brought up, and also after it is brought down, so WOL should work even if the network is not brought down correctly.

Sending WOL messages

I installed the etherwake package in the controlling system for the etherwake command to send the "Magic Packet" to my computer to wake it up. The program must be run as root to send the packet (I use sudo to execute it).

# aptitude install etherwake
# etherwake <mac address>

wakeonlan is also available, a program that uses UDP packets not TCP, and hence does not need to be run as root. It is also slightly more configurable.

# aptitude install wakeonlan && exit
$ wakeonlan <mac address>

WOL Sensitivity

I found that I didn't want any of the Wake On LAN settings except Wake on "Magic Packet" (g). I only wanted my machine to turn on when I specifically told it to, not on unicast messages (u), broadcast messages (b) or multicast messages (m).

However, if you do want Wake On LAN on any of these events (other than "Magic Packet"), you may find conflicts with pm-utils2. At the time of writing, scripts in this package will set the wake option for all relevant interface cards to "Magic Packet" only, (g). This will be a problem if you want your machine to wake "on-demand", when it receives traffic (u), for example. The issue and a fix is discussed below.

WOL Persistence

Hardware looks up to spec, you think the BIOS is set right, but it still doesn't work without some tweaking using the software. According to the Wake On Lan client FAQ most Linux drivers disable the WOL feature on boot3, so we need to get it going.

Kernel 2.6

With a 2.6 kernel we're using /etc/modprobe.d. You may be using /etc/modprobe.conf, but if it's not including /etc/modprobe.d you're probably getting told about that each time you boot and some stuff may not be configured properly. I'm using /etc/modprobe.d and I added a file local.conf into the directory. It says:

install 8139too /sbin/modprobe -i 8139too; /sbin/ethtool -s eth0 wol g

ethtool comes from the ethtool package, so you'll need to install that unless your card supports a load option to set WOL. If that's the case I'd make an local.conf file with the appropriate options line, maybe something like:

options 3c59x enable_wol=1

Testing on another machine with a C3905B-TXNM and a 3C905C-TXM that uses the 3c59x module to drive them both I found that ethtool was unable to query them or set the WOL setting, but that the enable_wol=1 setting did work and was required.

While I was messing with these settings, I noticed that both 8139too and 8139cp were loading, but loading just 8139cp alone failed since my chipset isn't new enough so I blacklisted it.

Debugging state with ethtool

After an hour struggling with why my system still didn't work I started throwing in the ethtool query command all over the place to see what the deal was:

# ethtool eth0


I found that (at least with my 8139too driver on Debian 3.1/Sarge) the install line was working when I'd modprobe 8139too, but ifup also resets the WOL setting, so I added an up line to /etc/network/interfaces under eth0:

iface eth0 inet dhcp
        up /sbin/ethtool -s $IFACE wol g

I kept the ethtool command in /etc/modprobe.d/local.conf in case I boot and ifup isn't executed before shutting down.

PM-Utils Conflicts

The pm-utils package contains scripts that are run on suspend, hibernate and on resume of the system. There is one script, /usr/lib/pmutils/power.d/disable_wol, which sets the configuration for interfaces to only wake on "Magic Packet" (g), regardless of the settings you may have configured in /etc/network/interfaces (or one of the files under /etc/network/interfaces.d, or manually using ethtool or in some other way). Look for lines in the file similar to the following:

            disable) ethtool -s "${d##*/}" wol d>/dev/null 2>&1;;
            enable) ethtool -s "${d##*/}" wol g>/dev/null 2>&1;;

Obviously, if you have set an interface to Wake on LAN in the event of a unicast packet or "Magic Packet" (ug), then suspend using pm-suspend, for example, this script will set the interface to "Magic Packet" only (g) as part of the suspension process.

You can detect the problem, once you know what you're looking for, by noticing through ethtool after a resume that the "Wake-on" settings for interfaces have been set to "g".

A simple fix (that will not interfere with package updates) is to add a file with the same name, disable_wol to the local configuration directory, /etc/pm/power.d/. This overrides the script in /usr/lib/pm-utils/power.d/disable_wol.

This is my (somewhat verbose, and functionally trivial) /etc/pm/power.d/disable_wol:

# Override the file /usr/lib/pm-utils/power.d/disable_wol which
# manually configures Wake On Lan (WOL) settings for interfaces.
# That default file uses ethtool to configure WOL for all interfaces
# to "g" (magic packet) alone.  
# Note that the presence of this file, with the same name but under
# /etc/pm/power.d/, is sufficient to completely override the file
# under /usr/lib/pm-utils/power.d/.  This latter file is included in
# the the "pm-utils" Debian package, and may be updated from time to
# time through the package-management system.  The directories under
# /etc/pm/ are the appropriate places for local configurations.
# On this system, the WOL configurations are made in the interface
# configuration under /etc/network/.  Each interface can have a 
# different configuration, and it is typical to configure WOL to 
# "ug" to wake the system on a unicast packet for traffic sent
# specifically to that interface.  This allows the system to be
# woken on demand, when traffic to one of its interfaces is received.

exit 0


Wake On LAN works on Debian and opens some new options up to me.

I can log into my gateway and boot my desktop, grab what I need and then power it back off remotely. I'm using DHCP with MAC-to-IP mappings so I can look in that file on my gateway system to know the MAC address of the system I wish to wake up. If I didn't have that I could keep a text file.

My next feat is to have non-essential systems power-off (not just halt) on a power outage to extend the battery runtime for the essential systems and then use WOL to power the other systems back on after power is restored and the battery has hit some specific charge level. I think some settings with halt or APM or ACPI are not right on those systems. See OffAndOnAgain.

CategoryNetwork | CategorySystemAdministration