What you can do to help:
If you can't connect to your favourite computer:
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.
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.
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.