Set up Wake-on-LAN on systemd

March 4, 2023

OR: How to Help Save the Earth, and save a couple bucks on your electric bill 🔗

PhotoStructure is (mostly) developed on an AMD Ryzen 9 5950X workstation.

It’s nice and speedy, but consumes 500+ watts when busy, and 200 watts at idle!

I can’t do much about the power consumption while I’m using it–but that idle consumption certainly could be reduced.

Suspend-to-RAM when idle 🔗

The latest version of Ubuntu (and my current motherboard) support “suspend to RAM” (much like a laptop). Configuration can be done via the built-in Settings app, which is simple and works. If you need more customization, Circadian is an excellent alternative.

Power drops to 2 watts (!!) when suspended to RAM.

Local wakeups 🔗

So, I come back to my workstation after my morning coffee, and it springs back to life when I hit a key on my USB keyboard. The system wakes up and is available in a couple seconds, and most things are right where I left them–except for Firefox, which regularly crashes, but all my prior tabs restore automatically when I re-launch Firefox.

Remote wakeups: how to enable Wake-on-LAN 🔗

The issue is if I’m remote, and I need access to my workstation.

Is it possible to remotely resume power on my workstation?

The answer is yes: Wake-on-LAN is a thing. Unfortunately, it typically requires a bit of tweaking.

Following the steps on the Ubuntu wiki, https://help.ubuntu.com/community/WakeOnLan:

Install ethtool (via sudo apt install ethtool)
Run ip link to get the name of your network device. Ignore lo (that’s the localhost LOopback device) and any named docker* or br* devices (those are for docker and bridge networking). Mine happens to be called enp5s0.
Run sudo ethtool $devicename | grep Wake (replace $devicename with the name of your device). You’ll see something like this:
```
  Supports Wake-on: pumbg
  Wake-on: d
```
The d means Wake-on is disabled. Read the ethtool man page for details.
If Supports Wake-on: includes g, we’re in business: we just need to set Wake-on: g after every powercycle. That’s done by running sudo ethtool -s $devicename wol g.

If you don’t see it, don’t panic: it may just be disabled in your BIOS. Reboot and hit f2/del/f12 to enter BIOS configuration, and poke around–mine was enabled via a Power submenu.

How to enable Wake-on-LAN on reboot 🔗

If you’ve read to here, you’ve enabled Wake-on-LAN on your hardware… but might have caught the bit about needing to run ethtool -s $devicename wol g after every reboot.

Simple, just add it to /etc/rc.local, right?

NOPE. That file’s been gone for over a decade on many linux distributions. Good idea, though ~~old man~~ wise neckbeard.

Ah, just follow the /etc/network/interfaces instructions on the Ubuntu wiki?

NOPE, that file doesn’t reliably exist since NetworkManager times.

SO… It’s gotta be something involving systemd, right?

CORRECT. Run sudo systemctl edit wol.service --full --force and paste this into the editor. Replace $deviceName with the name of your device.

[Unit]
Description=Enable Wake-on-LAN
Documentation=https://help.ubuntu.com/community/WakeOnLan
After=network-online.target

[Service]
Type=oneshot
ExecStart=/sbin/ethtool -s $deviceName wol g

[Install]
WantedBy=network-online.target

Check that there were no errors with sudo systemctl status wol.

If you need to tweak anything, you can re-enable the service with sudo systemctl enable --now wol.

Trust but verify 🔗

Verify this all worked by shutting down your computer, turning off the power supply for 10 seconds, then restarting (to make sure the physical network device isn’t retaining prior settings).

After rebooting, sudo ethtool $devicename | grep Wake should show

  Supports Wake-on: pumbg
  Wake-on: g

Get your MAC address 🔗

The MAC address is a unique identifier that is used by Wake-on-LAN client applications to send the “magic packet” that will wake up your workstation.

If you’re in Gnome, open the Settings app, select the Network tab, and click the gear by your wired network device.

Otherwise, run the ip link command, and look for the MAC address right after the “link/ether” line following your network device (remember to ignore the docker and bridge devices!)

Finally, send the magic packet 🔗

Suspend your workstation, either via the command-line with sudo systemctl suspend, or via the menu bar > Power off/log out > Suspend.

You should be able to wake your sleeping workstation via another computer on your LAN by using either the etherwake or wakeonlan commands (both can be installed via sudo apt install).

Alternatively, some routers have “network tools” that support sending Wake-on-LAN magic packets.