Wake-on-LAN for Linux

My sons upgraded their gaming computers last Christmas, and I ended up using their old parts to build a couple of Linux servers running Ubuntu servers. The idea is to use these extra servers as video encoders since they will have dedicated GPUs. However, the GPUs are also pretty power-hungry. Since they don’t need to be up 24 hours a day, I thought keeping these servers asleep until they are required would be good. At the same time, it would be pretty inconvenient to go to the servers to physically power them up when I needed them. The thought of configuring their Wake-on-LAN came to mind.

I found this helpful article online. I first found out that the Network Interface on the old motherboards supports Wake-on-LAN (WOL). Below is a series of commands that I executed to find out whether WOL is supported or not, and if so, then enable the support.

% sudo nmcli connection show
NAME                UUID                                  TYPE      DEVICE
Wired connection 1  d46c707a-307b-3cb2-8976-f127168f80e6  ethernet  enp2s0

% sudo ethtool enp2s0 | grep -i wake
	Supports Wake-on: pumbg
	Wake-on: d

The line that reads,

Supports Wake-on: pumbg

indicates the WOL capabilities, and the line that reads,

Wake-on: d

indicates its current status. Each letter has a meaning:

• d (disabled), or
• triggered by
  • p (PHY activity), 
  • u (unicast activity),
  • m (multicast activity),
  • b (broadcast activity), 
  • a (ARP activity),
  • g (magic packet activity)

We will use the magic packet method. Below are the commands used to enable WOL based on the magic packet trigger.

% sudo nmcli connection modify d46c707a-307b-3cb2-8976-f127168f80e6 802-3-ethernet.wake-on-lan magic

% sudo nmcli connection up d46c707a-307b-3cb2-8976-f127168f80e6
Connection successfully activated (D-Bus active path: /org/freedesktop/NetworkManager/ActiveConnection/2)

% sudo ethtool enp2s0 | grep -i wake
	Supports Wake-on: pumbg
	Wake-on: g

The above changes will persist even after the machine reboots. We put the machine to sleep by using the following command:

% sudo systemctl suspend

We need the IP address and the MAC address of the machine to wake the computer up using the wakeonlan utility.

% ifconfig
enp2s0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST>  mtu 1500
        inet 192.168.168.185  netmask 255.255.255.0  broadcast 192.168.168.255
        inet6 fd1a:ee9:b47:e840:6cd0:bf9b:2b7e:afb6  prefixlen 64  scopeid 0x0<global>
        inet6 fe80::41bc:2081:3903:5288  prefixlen 64  scopeid 0x20<link>
        inet6 fd1a:ee9:b47:e840:21b9:4a98:dafd:27ee  prefixlen 64  scopeid 0x0<global>
        ether 1c:1b:0d:70:80:84  txqueuelen 1000  (Ethernet)
        RX packets 33852015  bytes 25769211052 (25.7 GB)
        RX errors 0  dropped 128766  overruns 0  frame 0
        TX packets 3724164  bytes 4730498904 (4.7 GB)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0

We use the above ifconfig to find the addresses highlighted in bold. Once we have the required information, we can then wake the computer up remotely by executing the wakeonlan command from another computer.

% wakeonlan -i 192.168.168.255 -p 4343 1c:1b:0d:70:80:84
Sending magic packet to 192.168.168.185:4343 with 1c:1b:0d:70:80:84

Note that the above IP address used is the broadcast address and not the machine’s direct IP address. Now I can place these servers to sleep and only turn them on remotely when I need them.