Ubuntu's networking stack is constantly evolving and most previous information on enabling Wake-on-LAN for an interface is outdated (like the Ubuntu wiki).
Now that Ubuntu uses Netplan instead of /etc/network/interfaces, how do I enable Wake-on-LAN automatically whenever a particular interface comes up?
I fixed it by adding a file to /etc/netplan, named /etc/netplan/50-wol.yaml
the contents of the file are: (fill in your own mac-address).
network:
version: 2
renderer: NetworkManager
ethernets:
enp2s0:
match:
macaddress: XX:XX:XX:XX:XX:XX
wakeonlan: true
dhcp4: yes
The wiki tells us we need to run ethtool -s <interface> wol g when the interface comes up.
Although Ubuntu 20.04 has ifupdown scripts under /etc/network/if-up.d, Netplan provides different guidance on how to run post-up hook scripts that suggests using networkd-dispatcher.
The manual page for networkd-dispatcher does not explain how to detect which interface is going down but the source code shows several environment variables that get set including IFACE.
So we can create /etc/networkd-dispatcher/routable.d/50-wake-on-lan (and chmod +x it) with a script like this:
#!/bin/sh -eu
case "$IFACE" in
enp60s0)
ethtool -s <interface> wol g
;;
esac
For me really helped this post: https://forum.manjaro.org/t/troubles-with-setting-up-wol/24815/3
TLDR:
execute sudo systemctl disable tlp
TLP is for power management on laptops etc. It is unlikely that you will need TLP on a system that you want to be able to remotely start a machine.
After execution of the command above WoL became persistent and you don't need to apply netplan after every reboot.
