1. Introduction

To ask a question about low-carbon desktop computing please send an email to: greenit@oucs.ox.ac.uk .

1.3. Answers

How do I enable "wake-on-LAN" on a desktop computer?
Not all computers can be woken using the WOL service, and some computers are capable but have wake-on-LAN disabled. Wake-on-LAN can be enabled by changing a computers BIOS settings. Exactly how this is done varies between different models of computer. Energy Star provide an introduction to enabling wake-on-LAN on desktop computers.
Does turning a computer off each day make it more likely that a component will fail?
The computing service department at Oxford University can find no evidence to support this idea. Over a hundred classroom and Help Centre desktop computers have been turned on and off on a daily basis for the last five years, without there being any evidence that components are failing as a result.
How do I switch computers into low-power states?
There are many ways to switch desktop computers into low-power states: (a)manually switching a computer off, or into sleep (S3) and hibernate(S4) power-saving modes, (b) configuring sleep (S3) and hibernate (S4) so the computer and monitor automatically enter low-power states after a period of inactivity , (c) logging into a computer remotely, for instance using a 'remote desktop' type application, and shutting it down e.g. using the DOS command "shutdown -s", (d) installing a script such as PowerDown, developed at Liverpool University, to automatically switch computers off after a specific period of time if nobody is logged in.
Are there commercial service that support improved desktop power management?
Yes. EnergyStar have created a list of commercial services that support desktop power management initiatives. Like EnergyStar the computing service can offer no advice on the suitability of these service within departments and colleges at the University.
Is it more efficient to leave a computer on all the time, rather than boot it each morning, because booting computers uses so much electricity?
No. Booting a computer may raise the power that a computer is running at by a few Watts for around 90 seconds but the extra energy consumed is insignificant compared to the energy that will be consumed if left on over night.
Are other educational organisations undertaking similar initiatives?
Yes, here we list a few examples:
What do I need to do to install a gateway server 'behind' a NAT router?
The gateway can be set up to turn on computers on a private network, behind NAT. In order to allow this, certain requirements have to be fulfiled:
- the gateway needs to be a part of the private network both physically and logically
- NAT has to be configured to enable port forwarding to the gateway IP on port 8443 (any inbound packet sent to the public IP address of the NAT has to be forwarded on port 8443)
- it is essential, that the DNS name on the certificate for the gateway matches the DNS name of the public IP address of the NAT
How do I turn my computer off remotely e.g. when away at a conference or from home?
In case the usual route of turning your computer off remotely didn't work on your Windows machine, you can go to Start -> Run and issue the command: "shutdown.exe -s". You will be prompted with a warning and the system will take 30 seconds to shut down. You can create a shortcut to the command and put it on the desktop, to make the shutdown process quicker and easier. On Linux machines, issue the following command to turn the computer off: "shutdown -h now"
I think that my local firewall is blocking the WOL packets, as my computers never wake up. How can i help this?
If you use a local firewall within the WOL subnet, it may stop the magic packets in circulating and waking computers up. In order to address the problem, make sure, that the firewall is set to allow UDP traffic on port 9 originating from your WOL gateway.
I installed the Linux-based gateway VM image in my Virtual Infrastructure, but can't connect to it via SSH. Can you help?
The Linux VM images have very tight security and by default, all incoming connection are blocked. In order to allow incoming SSH sessions, edit the following files allowing connections to port 22 from your management IP: /etc/hosts.allow and /etc/init.d/iptables. This article explains how to use iptables to get the desired effect.
Can WoL work on a VMPS network?
WoL and Dynamic VLANs are not compatible because when the PC is shut down, the NIC will be powered down for a split second. This causes the switch to detect the link-down event and to un-assign the port. When the NIC comes back online, the port does not belong to any VLAN and since no frames are received by the port, it would never initiate VMPS queries or forward broadcast/multicast to the device connected to it.
Are there any known conflicts with other software?
We have discovered, that FiDo software causes conflicts when run alongside of Altiris and VMware software. The conflict is related to ports - Altiris and VMware use the same ports as the gateway software. To avoid running into such problems, we advise to designate a separate computer to act as FiDo gateway.
Is it possible to set up scheduled wake up for multiple computers/devices?
A scheduled wake up of multiple computers can be achieved - computers/devices have to be added to a group first, using the ITSS Wake-on-LAN pages available here.

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