16.7. WOL – Wake On LAN

WOL (Wake on LAN) refers to the possibility of “waking up” a computer from standby mode over the network, using special packages. This “magic packet” is received by the network card and ensures that the motherboard activates the power supply to the power source and boots the computer.

The advantage of this method is that computers do not have to be permanently switched on (which saves energy), yet they can be activated via WOL.

[Important]Support for WOL

Wake on LAN only works with more recent motherboards which support this functionality in their BIOS. WOL-capable network cards mostly contain chips in the Intel i82557 (EEpro100B), i82558 (EEPro100+) or i82559 series. Further information on this is available from http://support.intel.com/support/network/sb/cs-008459.htm.

Unfortunately, a lot of hardware does not have this functionality, even though it is apparently WOL-capable. Unfortunately, there is no alternative but to try out the relevant steps.

16.7.1. BIOS Configuration

Before you use WOL, you need to enable an option in BIOS which is frequently labeled OnBoard LAN or Boot from LAN. Depending on your particular variant of BIOS, it can be found in the OnBoard Device Configuration, Boot or PowerSave menu. In case of doubt, consult the documentation for your motherboard.

You should further check that your server has the latest BIOS and, if necessary, update it. Information on BIOS updates can be found on the homepage of the relevant motherboard vendor.

[Warning]BIOS updates

A BIOS update is tricky to implement. It is therefore imperative that you stick closely to the instructions issued by your motherboard vendor, as otherwise your motherboard could become inoperable and your server could no longer start up.

Older network cards (for example, 3COM) have to be connected to the motherboard with a 3-pin cable. On newer network cards, this procedure is no longer necessary.

16.7.2. Configuration With YaST

Start up YaST as root user and call the module via menu selection Network Services+WOL. If there is a DHCP server running on your computer, the WOL module will display the existing computers on your network which you can include in your WOL list.

If a DHCP server is not running, then you will have to enter the remote computers manually. Click Add and enter the host name and MAC (Media Access Connector) address for the network card. The MAC address is unique for every network device and can be displayed through the following call:

# ip link show eth0
2: eth0: <BROADCAST,MULTICAST,NOTRAILERS,UP> 
mtu 1500 qdisc pfifo_fast qlen 1000
    link/ether 00:80:c8:94:c3:e7 brd ff:ff:ff:ff:ff:ff

In the Enter the MAC Address of the client: field, enter the value contained in link/ether. Confirm with Save. The configuration with YaST is now complete.

16.7.3. Waking Up Computers

If your computers are appropriately configured, you can wake them up in the WOL YaST module by clicking Wake up. The selected computer will then start up.

Another option is to enter the command ether-wake from the netdiag package. With this command, a particular computer can be woken up by entering its MAC address, as follows:

# ether-wake 00:80:C8:94:C3:E7

You can obtain help on this command through --help or -u.

16.7.4. Further Information

Further information is available in the mini HOWTO for WOL at http://gsd.di.uminho.pt/jpo/software/wakeonlan/mini-howto/wol-mini-howto.html.