Computer Laboratory

Power saving on Linux systems

To save power on Linux systems, shut them down when not in use. This is not a problem for machine management.

Most window managers have commands to suspend, hibernate or shudown a machine, but you can also use shell commands such as "cl-asuser pm-suspend", "cl-asuser pm-hibernate" and "cl-asuser shutdown -h now". Get the machine to a "safe" state before trying a command, as it may fail to fully shut the machine down, or the machine may not fully resume, so it may be necessary to power cycle the machine.

While off, consider using the time sharing systems, or if the machine is needed, boot it via the web.

The package cl-isidle should be used to try to detect when a user has forgotten to shutdown a machine, and act as a backstop. It tries to detect an "idle" machine, typically when a number of sucessive polls find that the sum of the three load averages is below 0.6 and there is no logged in user, or no logged in users who have been idle for less than an hour. It can be tailored not to poll certain times of the day, such as "office hours". It will try to suspend, hibernate or shutdown the machine. It will try to improve the chances of keeping Kerberos tickets available by refreshing them before shutdown and after resumption, but if the tickets are stores in /tmp on distribution such as Ubuntu, they may be removed if it reboots (rather than resumes).

See "cl-isidle -h" for more details. There are a number of ways to change the behaviour of a machine, so if you would like to. please contact sys-admin.