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 labelled "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
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 /usr/sbin/ethtool -s $IFACE wol g post-down /usr/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.
You can then power down your system, and prepare the other system to wake it.
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>
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).
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 boot2, so we need to get it going.
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 install.local into the directory. It says:
install 8139too /sbin/modprobe -i 8139too; /usr/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 options.local file with the appropriate options line, maybe something like:
options 3c59x enable_wol=1
If your kernel uses an initramfs image (eg. Debian stock kernels), also run update-initramfs -u (or update-initramfs -u -k all if necessary) to rebuild kernel initial ramdisk(s).
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.
The forcedeth driver in kernel 2.6.18 (in Etch) does something strange and you have to send a reversed MAC address. If your MAC address were 00:11:22:33:44:55, you would type:
# etherwake -D 55:44:33:22:11:00
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 /usr/sbin/ethtool -s $IFACE wol g
I kept the ethtool command in /etc/modprobe.d/install.local in case I boot and ifup isn't executed before shutting down.
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.
Using Wake-On-LAN WOL/PME to power up your computer remotely