ethtool, WOL: What does "wake on physical activity" actually mean and (how) can I use it?


I am fighting with the WOL settings of my Ubuntu box at the moment. The idea is to have an HTTP/SVN server to sleep while it's unused and wake up when it's accessed. So far, wake-on-LAN works and is activated on startup:

Settings for eth1:
        Supported ports: [ TP ]
        Supported link modes:   10baseT/Half 10baseT/Full
                                100baseT/Half 100baseT/Full
        Supports auto-negotiation: Yes
        Advertised link modes:  Not reported
        Advertised pause frame use: No
        Advertised auto-negotiation: Yes
        Speed: 1000Mb/s
        Duplex: Full
        Port: Twisted Pair
        PHYAD: 0
        Transceiver: internal
        Auto-negotiation: on
        MDI-X: Unknown
        Supports Wake-on: pg
        Wake-on: pg
        Current message level: 0x0000003f (63)
        Link detected: yes

As you can see, I also set the wol p flag ('wake on physical activity'). My assumption was that I could convince the device to wake up not only on magic packets, but on any network access. This, however, seems to be wrong.

What does this flag mean then, and: (How) can I misuse this for my evil plans?

asked on Super User Oct 31, 2010 by sunside • edited May 19, 2011 by sunside

2 Answers


Note: the question is a 4+ year old cross post from here. Not sure why it gets a bounty after more than 4 years, but probably it received a wol package ;-)

The ethtool manual says:

wol p|u|m|b|a|g|s|d...
          Set Wake-on-LAN options.  Not all  devices  support  this.   The
          argument  to  this  option  is a string of characters specifying
          which options to enable.
          p  Wake on phy activity
          u  Wake on unicast messages
          m  Wake on multicast messages
          b  Wake on broadcast messages
          a  Wake on ARP
          g  Wake on MagicPacket(tm)
          s  Enable SecureOn(tm) password for MagicPacket(tm)
          d  Disable (wake on nothing).  This option clears  all  previous

The PHY activity refers to the PHY chip, that handles communication on the physical layer of the OSI model. In laymans terms: any package directly send to this networking device should wake the machine up.

The following conditions should be met before wake on PHY works:

  • your networking device supports this and your networking driver supports this. I'm not sure if ethtool is checking this extensively before setting the parameter. Check your manual/spec's to see if this specific feature is supported.
  • your ethernet card is still on after shutdown (led lights should be on). If this isn't the case, make sure that your OS isn't shutting down the card (in most Linux distro's put NETDOWN=no in /etc/default/halt).
  • wol settings are preserved after sleep/shutdown.
  • wol is enabled in your BIOS settings.

Also note that the default arp timeout is 30 seconds (also see this SU post). After that, the ip address of your target machine will be forgotten by the machine from where you are sending any physical package. Make sure you set a static arp address on the machine from where you are sending the package.

Now any directed request (ping, http, ssh, a wol package, ...) should bring your machine up.

answered on Super User Feb 24, 2015 by agtoever • edited Apr 13, 2017 by Community

I think your assumption is correct. There are many different events you can configure your device to wake up from. The documentation on ethtool isn't very clear on the p flag unfortunately.

A few questions that could help to analyze the problem: When your machine is shutdown, can you confirm that the network card is still running (LEDs blink) ? Are you trying to wake up your machine from within the same subnet or over a router ? How are you trying to wake it up? Can you use a network sniffer (wireshark) on the same network to confirm that data is actually sent on the subnet?

answered on Super User Nov 1, 2010 by pgruetter

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