In-house use of electric energy is a significant part of our overall ecologic footprint. Although behavioral changes will not reduce the overall footprint by a large factor every kWh is worth being saved if not needed. Hence we ask all CRC members to avoid wasting energy. There are simple steps that should be automatically followed every day.

Illumination

Always switch off the room lights when not needed. This applies to toilets, offices and corridors. Unfortunately it happens too often, that the light is kept on for a whole light or even weekend without anyone noticing. This is easy to avoid.

The energy saving is considerable. Our officies have standard lamps of 2x35W, with 4 lamps in small offices and 12 lamps in large officies. In 14h absence this corresponds to a saving of 3.9kWh=1.57€ for the small offices and 11.8kWh=4.7€ for the large offices.

Computers

Switch off idle computers, in particular when not being in the office. To allow for computers being switched off during weekends and other off-times but still allow for remote access in case of unplanned situations or other cases of a need for remote access set up Wake-On-Lan so that you can boot the computers remotely.

Here comes a step-by-step manual if your computer runs under Ubuntu (thanks to Leonard Kaiser for collecting this):

Wake on LAN with Ubuntu

With Wake on LAN (WoL), a PC can be started remotely from the local LAN network, by sending a so-called “Magic Packet” to the MAC address of its Network Interface Controller (NIC).

BIOS settings

In your BIOS, search for “Power on by PCI-E”, “Wake up on PCI event”, “Wake up on LAN” or similar and enable Wake on LAN.

Older PCs may not have a WoL option in the BIOS. They may either not support WoL at all or require connecting physical cables to enable it.

NIC name

To find out the name of your NIC, use ip link to show the name of all available adaptors.

For me, those were lo and enp0s31f6, where the latter is the NIC and lo the loopback device. In the following, the NIC name is replaced by NIC.

Activate WoL

For this, we need the ethtool command, to be installed with sudo apt-get install ethtool. Using

sudo ethtool NIC

we can determine the current settings by looking at the letters listed for the properties Supports Wake-on and Wake-on. Their meaning is explained in man ethtool:

wol p|u|m|b|a|g|s|f|d...
                  Sets Wake-on-LAN options.  Not  all  devices  support  this.
                  The argument to this option is a string of characters speci‐
                  fying which options to enable.

                  p   Wake on PHY activity
                  u   Wake on unicast messages
                  m   Wake on multicast messages
                  b   Wake on broadcast messages
                  a   Wake on ARP
                  g   Wake on MagicPacket™
                  s   Enable SecureOn™ password for MagicPacket™
                  f   Wake on filter(s)
                  d   Disable (wake on  nothing).   This  option
                      clears all previous options.

If the letters after Wake-on contain d, WoL needs to be activated. This can be done manually by running sudo ethtool -s NIC wol g after each boot, but we can also automate this:

Create the file /etc/systemd/network/50-wired.link with contents

[Match]
MACAddress=aa:bb:cc:dd:ee:ff
[Link]
NamePolicy=NIC
MACAddressPolicy=persistent
WakeOnLan=magic

where aa:bb:cc:dd:ee:ff is the MAC address of the NIC and NIC its name, both obtainable using the ifconfig command.

Using Wake on LAN

With the above configuration completed, the PC can be woken by another PC in the same LAN network. For this, we can use hera. Without sudo rights, we can use the wakeonlan command:

wakeonlan -i aaa.bb.ccc.dd aa:bb:cc:dd:ee:ff

where aaa.bb.ccc.dd is the IP address of your PC. Executing this will send the Magic Packet to your PC and start it up.

WoL after Standby or Suspend

If using standby or suspend, you may experience that WoL is not working afterwards. To remedy that, add the entry networking to the property STOP_SERVICES in the /etc/default/acpi-support file:

# Add services to this list to stop them before suspend and restart them in
# the resume process.
STOP_SERVICES="networking"

If STOP_SERVICES already contained entries, separate networking with a space.

Resources

https://help.ubuntu.com/community/WakeOnLan https://wiki.ubuntuusers.de/Wake_on_LAN/ (german)