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How to configure the Linux kernel/Power management options (ACPI, APM)

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Power management options (ACPI, APM)Edit

APM (Advanced Power Management) BIOS SupportEdit

    • depends on PM && !X86_VISWS

  • Option: APM
    • Kernel Versions: ...
    • (on/off/module) APM (Advanced Power Management) BIOS support
    • depends on PM && PM_LEGACY
      APM is a BIOS specification for saving power using several different techniques. This is mostly useful for battery powered laptops with APM compliant BIOSes. If you say Y here, the system time will be reset after a RESUME operation, the /proc/apm device will provide battery status information, and user-space programs will receive notification of APM "events" (e.g. battery status change).
      If you select "Y" here, you can disable actual use of the APM BIOS by passing the "apm=off" option to the kernel at boot time.
      Note that the APM support is almost completely disabled for machines with more than one CPU.
      In order to use APM, you will need supporting software. For location and more information, read <file:Documentation/pm.txt> and the Battery Powered Linux mini-HOWTO, available from <>.
      This driver does not spin down disk drives (see the hdparm(8) manpage ("man 8 hdparm") for that), and it doesn't turn off VESA-compliant "green" monitors.
      This driver does not support the TI 4000M TravelMate and the ACER 486/DX4/75 because they don't have compliant BIOSes. Many "green" desktop machines also don't have compliant BIOSes, and this driver may cause those machines to panic during the boot phase.
      Generally, if you don't have a battery in your machine, there isn't much point in using this driver and you should say N. If you get random kernel OOPSes or reboots that don't seem to be related to anything, try disabling/enabling this option (or disabling/enabling APM in your BIOS).
      Some other things you should try when experiencing seemingly random, weird problems:
      1) make sure that you have enough swap space and that it is enabled. 2) pass the "no-hlt" option to the kernel 3) switch on floating point emulation in the kernel and pass the "no387" option to the kernel 4) pass the "floppy=nodma" option to the kernel 5) pass the "mem=4M" option to the kernel (thereby disabling all but the first 4 MB of RAM) 6) make sure that the CPU is not over clocked. 7) read the sig11 FAQ at <> 8) disable the cache from your BIOS settings 9) install a fan for the video card or exchange video RAM 10) install a better fan for the CPU 11) exchange RAM chips 12) exchange the motherboard.
      To compile this driver as a module, choose M here: the module will be called apm.

    • Kernel Versions: ...
    • (on/off) Ignore USER SUSPEND
    • depends on APM
      This option will ignore USER SUSPEND requests. On machines with a compliant APM BIOS, you want to say N. However, on the NEC Versa M series notebooks, it is necessary to say Y because of a BIOS bug.

  • Option: APM_DO_ENABLE
    • Kernel Versions: ...
    • (on/off) Enable PM at boot time
    • depends on APM
      Enable APM features at boot time. From page 36 of the APM BIOS specification: "When disabled, the APM BIOS does not automatically power manage devices, enter the Standby State, enter the Suspend State, or take power saving steps in response to CPU Idle calls." This driver will make CPU Idle calls when Linux is idle (unless this feature is turned off -- see "Do CPU IDLE calls", below). This should always save battery power, but more complicated APM features will be dependent on your BIOS implementation. You may need to turn this option off if your computer hangs at boot time when using APM support, or if it beeps continuously instead of suspending. Turn this off if you have a NEC UltraLite Versa 33/C or a Toshiba T400CDT. This is off by default since most machines do fine without this feature.

  • Option: APM_CPU_IDLE
    • Kernel Versions: ...
    • (on/off) Make CPU Idle calls when idle
    • depends on APM
      Enable calls to APM CPU Idle/CPU Busy inside the kernel's idle loop. On some machines, this can activate improved power savings, such as a slowed CPU clock rate, when the machine is idle. These idle calls are made after the idle loop has run for some length of time (e.g., 333 mS). On some machines, this will cause a hang at boot time or whenever the CPU becomes idle. (On machines with more than one CPU, this option does nothing.)

    • Kernel Versions: ...
    • (on/off) Enable console blanking using APM
    • depends on APM
      Enable console blanking using the APM. Some laptops can use this to turn off the LCD backlight when the screen blanker of the Linux virtual console blanks the screen. Note that this is only used by the virtual console screen blanker, and won't turn off the backlight when using the X Window system. This also doesn't have anything to do with your VESA-compliant power-saving monitor. Further, this option doesn't work for all laptops -- it might not turn off your backlight at all, or it might print a lot of errors to the console, especially if you are using gpm.

  • Option: APM_RTC_IS_GMT
    • Kernel Versions: ...
    • (on/off) RTC stores time in GMT
    • depends on APM
      Say Y here if your RTC (Real Time Clock a.k.a. hardware clock) stores the time in GMT (Greenwich Mean Time). Say N if your RTC stores localtime.
      It is in fact recommended to store GMT in your RTC, because then you don't have to worry about daylight savings time changes. The only reason not to use GMT in your RTC is if you also run a broken OS that doesn't understand GMT.

  • Option: APM_ALLOW_INTS
    • Kernel Versions: ...
    • (on/off) Allow interrupts during APM BIOS calls
    • depends on APM
      Normally we disable external interrupts while we are making calls to the APM BIOS as a measure to lessen the effects of a badly behaving BIOS implementation. The BIOS should reenable interrupts if it needs to. Unfortunately, some BIOSes do not -- especially those in many of the newer IBM Thinkpads. If you experience hangs when you suspend, try setting this to Y. Otherwise, say N.

    • Kernel Versions: ...
    • (on/off) Use real mode APM BIOS call to power off
    • depends on APM
      Use real mode APM BIOS calls to switch off the computer. This is a work-around for a number of buggy BIOSes. Switch this option on if your computer crashes instead of powering off properly.

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