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2/29/2008
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Fight The Power: Greening Your Linux Systems

Linux has a lot of advantages as a desktop operating system. Power management, unfortunately, still is not one of them. But there are plenty of ways to make a Linux system less power-hungry -- and some of the most effective fixes are also some of the easiest.

Linux has a lot of advantages as a desktop operating system. Power management, unfortunately, still is not one of them. But there are plenty of ways to make a Linux system less power-hungry -- and some of the most effective fixes are also some of the easiest.Let Sleeping CPUs Lie. Older versions of the Linux kernel used a system timer that constantly wakes an idle CPU out of its power-saving mode, driving up a system's power usage. Version 2.6.21 of the Linux kernel, released last year, was the first to adopt what is known as "tickless idle," allowing an idle CPU to sleep a lot more of the time.

Of course, there are better reasons to keep all of your desktop software up to date -- especially if you don't like the idea of hanging virtual "hack me" signs from your company's PCs. And until you kick the old Linux kernel's timer-tick habit, most of the other power-saving tips you try aren't likely to do much good.

Knowledge Is (Less) Power. Some desktop Linux apps are designed to use the CPU and other hardware as efficiently as possible. Other apps -- probably most of them -- are hard-core power pigs. The trick is to know which software falls into the latter category, just how much power these apps are consuming, and how best to whip them into shape.

On a Linux laptop system, or most other Linux systems using a mobile chipset, a tool called PowerTOP can help you get to the bottom of this problem. PowerTOP provides a good summary of a system's power consumption, showing how much time a CPU spends in various idle states, how many times per second the CPU is getting called out of its sleep state, and (assuming the laptop is not running on AC power) how much battery time remains. PowerTOP also lists the top 10 sources of power consumption on a system, including hardware interrupts (which often occupy the top few spots), system services, and desktop software.

Better yet, PowerTOP also offers suggestions on how to deal with power-hogging software, including additional Linux kernel configuration tweaks or fixes for unruly desktop apps. Some of these suggestions involve changes that are easy enough for most Linux users to make; others require a higher comfort level working at the command line and editing config files. PowerTOP can also reveal a number of bugs that eat up CPU cycles or other hardware resources; some of these bugs have patches available, although others do not.

You can learn more about PowerTOP, including tips on using the tool and documentation, at LessWatts.org.

Surf Smart. Wireless networking hardware sucks down power like a vampire in a blood bank. That includes the nifty little Bluetooth gadget that you haven't touched since the day you bought your laptop (admit it, you know it's true) -- even when you don't actually use your WiFi and Bluetooth hardware, these devices' built-in radio transmitters can still consume an, umm, shocking amount of power.

If you don't use Bluetooth, disabling it should be one of your first power-management tasks. Chances are, you will have check your system documentation to find out how to do this, but I can (almost) guarantee that it will be about as easy a command-line encounter as you will ever see. Shutting off your WiFi radio transmitter when you're not using it is almost certainly even easier: Most laptop systems have dedicated hotkeys that turn the WiFi radio on and off.

Want To Know More? Obviously, I'm just scratching the surface with these suggestions. If you want more information on Linux power management, including plenty of tips, tricks, and free software downloads, the LessWatts.org Web site is by far the most comprehensive -- and, just as important, most up to date -- online resource. Just how much battery life you add to a laptop or how much money you save on your company's power bills will vary, of course, but don't be surprised if a few hours of research on this topic delivers some significant results.

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