HowTo: Enable Wake-on-LAN on CentOS / SL 6.3

Wake-on-LAN also know as WOL is the ability to switch on a computer that is connected to a network (local or not) by means of a special network message called a magic packet. This magic packet contains the MAC address of the destination computer. If the destination computer has a network interface card that support WOL then the system wakes up.

In this post I'll describe how to setup a CentOS destination computer so that it can be turned on from another computer. This procedure is also applicable to RHEL and its clones such as Scientific Linux and Oracle Unbreakable Linux.

For sake of simplicity I've broken down the procedure into a few steps:
1) Enable WOL in BIOS
2) Collect network interface information
3) Enable WOL for the next shutdown
4) Make WOL always enabled
5) Wake up the computer from local network
6) Wake up the computer from internet
7) Troubleshooting

1) Enable WOL in BIOS

These days pretty much all integrated or otherwise NICs support Wake-on-LAN, however more often than not you'll need to enable it in the BIOS. There are literally hundreds of BIOS around but look for the typical options: "Enable Wake-on-LAN", "Enable Wake on PCI" and "Enable Power of PCIE Devices".

2) Collect network interface information

Start by checking if the destination computer network card support Wake-on-LAN with ethtool:

1. $ ifconfig
eth0      Link encap:Ethernet  HWaddr 00:11:AA:22:BB:22 
          inet addr:192.168.1.5  Bcast:192.168.1.255  Mask:255.255.255.0
          inet6 addr: fc70::151:8daa:fbab:f14a/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:563668 errors:0 dropped:0 overruns:0 frame:0
          TX packets:317604 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000
          RX bytes:813741621 (776.0 MiB)  TX bytes:68592900 (65.4 MiB)
          Interrupt:22 Base address:0xa000

lo        Link encap:Local Loopback 
          inet addr:127.0.0.1  Mask:255.0.0.0
          inet6 addr: ::1/128 Scope:Host
          UP LOOPBACK RUNNING  MTU:16436  Metric:1
          RX packets:8 errors:0 dropped:0 overruns:0 frame:0
          TX packets:8 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0
          RX bytes:480 (480.0 b)  TX bytes:480 (480.0 b)
2. $ su
3. # ethtool eth0
Settings for eth0:
    Supported ports: [ MII ]
    Supported link modes:   10baseT/Half 10baseT/Full
                            100baseT/Half 100baseT/Full
    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: d
    Link detected: yes

The "Supports Wake-on: g" string means that the NIC does in fact support Wake-on-LAN while "Wake-on: d" is a sign that the feature is not turned activated in the operating system.

Do notice that the target of ethtool was eth0 which is my destination computer's network interface name.

To use Wake-on-LAN we need to identify the NIC MAC address to which end ifconfig can be used:

1. # ifconfig | grep HWaddreth0 Link encap:Ethernet HWaddr 00:11:AA:22:BB:22

 

3) Enable WOL for the next shutdown

To command the operating system to enable WOL for the eth0 network interface run:

1. # ethtool -s eth0 wol g

Issuing ethtool again now returns "Wake-on: g" so now we have WOL enabled:

1. # ethtool eth0
Settings for eth0:
    Supported ports: [ MII ]
    Supported link modes:   10baseT/Half 10baseT/Full
                            100baseT/Half 100baseT/Full
    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

4) Make WOL always enabled

To have WOL always enabled the operating system needs to be told that eth0 (this is my NIC's interface name, don't forget to change according to your own system) WOL is supposed to be active.

There are 2 methods to achieve this, one employs adding ethtool -s eth0 wol g command to /etc/rc.d/rc.local while the other consists in creating a network script and enabling the network service.

Choose one of the methods, personally I'd go for the /etc/rc.d/rc.local method as it requires less typing ;)

Method A

1. #echo '/usr/sbin/ethtool -s eth0 wol g' >> /etc/rc.d/rc.local

Method B

1. # vim /etc/sysconfig/network-scripts/ifcfg-eth0
DEVICE=eth0
TYPE=EThernet ONBOOT=yesETHTOOL_OPTS="wol g"
2. # chkconfig network on

5) Wake up the computer from local network

From the computer that will be used to send the magic WOL packet, install and run wakelan:

1. # yum install wakelan
2. # rehash
3. # wakelan 00:11:AA:22:BB:22

6) Wake up the computer from internet

This involves enabling port forwarding of UDP port 9 to the destination computer in the router's administration webpage. To fully benefit from WOL you should configure a dynamic DNS service.

Afterwards to issue the wake up command you can use websites such as http://wakeonlan.me, Android applications (Wake on Lan) or any other Wake-on-LAN application (every Unix-like system as an alternative available). Just make sure to use your dynamic DNS provided address and the destination computer's MAC.

7) Troubleshooting

While troubleshooting Wake-on-LAN I've noticed that if you use GRUB without timeout set and poweroff the computer while on the operating system selection menu, the next time you try to use Wake-on-LAN it won't work. So make sure you have GRUB with a timeout set (which is the case will all default installation of GRUB).

If the computer is disconnected from the power supply you'll need to boot the computer and turn off again so that the NIC assumes the WOL definitions.