How to Enable Advanced Power Management on a Linux* Laptop

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Challenge

Activate support for Advanced Power Management (APM) on a laptop running Linux*. With the help of APM, the CPU can tell the BIOS when it is appropriate to take steps automatically such as reducing the CPU clock, turning off the hard disk, turning off the display's backlight, etc. in order to save power.

Solution

Recompile the Linux kernel and make the appropriate BIOS settings to enable APM.

Basic guidelines about how to recompile the kernel are available in the kernel HOWTO. When the configuration script reaches the "character devices" section, the settings for full APM BIOS support in kernel version 2.0.30 or higher are as follows:

  • Advanced Power Management BIOS support: Yes
  • Ignore USER SUSPEND: No
  • Enable PM at boot time: Yes
  • Make CPU Idle calls when idle: Yes
  • Enable console blanking using APM: Yes
  • Power off on shutdown: Yes

 

Note: Many users choose not to enable console blanking, because it can cause problems with the current version of XFree* 3.2: The symptoms are that the screen will be blank when X starts, and it can usually be fixed simply by hitting a key. This small but annoying problem can also adversely affect the life of the display backlight.

Please read the configuration script's help texts for detail about what each option does. If your system does not fully support the APM BIOS standard, some of those options might crash your system. Test all APM features with the new kernel to make sure that everything works as it should.

After recompiling the kernel, do not forget to recompile the Linux PCMCIA drivers as well. The precompiled PCMCIA drivers that come with most Linux distributions have APM support disabled, so that the BIOS cannot instruct your card adapters to turn off.

You must also recompile the drivers if you upgrade to a new kernel version and your old kernel was compiled with module version information turned on (this option is found in the "loadable module support" section of the kernel configuration).

Note: Not all manufacturers implement a correct APM BIOS, so some laptops have trouble with the Linux APM drivers (if your machine has trouble with APM, it will most likely either lock up at Linux boot up or after returning from suspend). If you are not sure, check the Linux laptop page for your specific model.

Source

Enabling Advanced Power Management on a Linux* Laptop

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