Energy Saving in the Statistical Laboratory

Quick Start

To save energy:

Linux desktops which are not exporting data spaces turn themselves off when they have been idle and unused for half an hour.
Windows desktops which are idle for a certain time period will go into hibernation whether or not anyone is logged in. Generally this time period is 75 minutes during core hours (08:00-18:00 Mon-Sat) and 20 minutes out of core hours.

What you can do to help:

Switch off monitors when they are not in use
When switching off Windows computers, shut them down via the "Sleep, Shutdown or Reboot" icon
When switching off Linux computers, use the ``safeshutdown'' command
When restarting Linux computers, use ``safereboot''
If your computer crashes or won't turn on, tell help@maths (we won't notice unless we have cause to turn it on ourselves)
General tips on saving energy at work

If you can't connect to your favourite computer:

If you just want to check your email, use the Statslab webmail service or ssh into martha or primrose
For more intensive work, wake up your machine online or use the wake command from another machine

Overview

Monitors and other computer peripherals such as speakers and office printers can be turned off whenever they are not in use, as can Windows computers (shutting them down via Windows is preferable to pressing the power switch).

In the past, you may have been told not to turn Linux computers off, for a couple of reasons. First, a remote user might be using the PC or running a job on it when it was shut down, and second, they might wish to log in while the computer was off and find themselves unable to do so.

However, there are now solutions to these problems - the ``safeshutdown'' command will check whether a Maths machine is idle before powering it down, and machines can be woken up remotely via Wake-on-LAN. Therefore the SL6 computers will shut themselves down when they have been idle and unused for half an hour.

Shutting Down Linux Computers

The best way to shut down a computer on the Maths network is to type ``safeshutdown'', a local command which will automatically check that the computer is idle before powering it off. Note that Linux will only let you shut a computer down when you are actually sitting at it, not when you are logged in remotely. ``safereboot'' is a similar command which will restart only idle computers, useful if your computer seems to have got into a mess.

Those of you who use Linux machines outside the CMS may find it useful to know how they can check whether a computer is in use themselves. One way is to type ``w'' into a terminal window. The output will look like this:

 10:30:57 up 14 days, 45 min,  3 users,  load average: 0.02, 0.10, 0.08
USER     TTY      FROM              LOGIN@   IDLE   JCPU   PCPU WHAT
eva      :0       -                08:59   ?xdm?  48:42   0.16s -/bin/tcsh -c /
eva      pts/2    :0.0             08:59    0.00s  0.07s  0.01s w
eva      pts/1    :0.0             08:59   21:47   0.54s  0.02s ssh ermyers@chi

The ``load average'' mentioned in the first line is a measure of how heavily loaded the computer is. (The three numbers are the load averages for the last 1, 5, and 15 minutes.) If any of these numbers is over 0.5, someone is probably running a long job on your computer, and it should be left on.

The remaining lines indicate who is logged onto the computer, where they are logged on from, when they logged on, and what they are doing. They contain a lot of information in a very small space, but for the purpose of determining whether the computer is in use, you need only look at the first column. If you see any login name other than your own, that person is using the computer, and it must be left on.

In the example above, the computer is unloaded and no-one but me is using it, so I could safely shut it down to save power. On most standard Linux machines this is done by selecting ``Shut Down'' from the System menu or typing ``poweroff'', but these have been disabled on the Maths machines to reduce the risk of accidentally shutting down a machine which someone else is using.

Waking Up Linux Computers

You may find that your favourite computer is switched off when you want to connect to it from home. It is a good idea to use the ``ping'' command to check before connecting. You can either do your work on an alternative computer (martha and primrose are always on) or wake up your computer via the web.

If you have a recurring problem with ``your'' computer being down when you want to use it, there are several options. For light use such as checking email you can simply use martha or primrose. You can leave yourself logged in to your favourite computer at all times so that it never shuts down automatically. Technically savvy users can run their own cron jobs on martha or primrose to wake up their computer at a time which suits them (the command to run is "wake" e.g. "wake solstice").

If you want to wake up some computers in order to run a number-crunching job, then this list of computers and their specs may be of interest to you.