12.18. Advanced Power Management - APM

12.18.1. Linux Compatibility Check

Start by reading the Battery-Powered-mini-HOWTO.

For APM to work the machine's firmware must implement the APM Specification. Linux supports versions 1.0 through 1.2 of the standard. To work with Linux the APM BIOS must support 32-bit protected mode connections.

To display information about the APM BIOS on your system you can run dmesg | grep apm command or look in the /proc/apm file.

12.18.2. Introduction

APM support consists of two parts: kernel support and user-land support.

12.18.3. Caveats

If you use another operating system at the same computer make sure that its "suspend" and "hibernate" features don't write to partitions that are used by Linux.

12.18.4. Troubleshooting

If your machine worked with 2.0.x kernels but not with the 2.2.x series, take this advice from Klaus Franken kfr_AT_klaus.franken.de : "The default changed in 2.2. Search in the init-scripts for halt and change it to halt -p or poweroff. See man halt , if you don't have this option you need a newer version of halt." You may find it in the SysVinit package.

On some new machines (for instance HP Omnibook 4150 - 366 MHz model) when accessing /proc/apm, you may get a kernel fault general protection fault: f000. Stephen Rothwell explaines: "This is your APM BIOS attempting to use a real mode segment while in protected mode, i.e. it is a bug in your BIOS. .. We have seen a few of these recently, except all the others are in the power off code in the BIOS where we can work around it by returning to real mode before attempting to power off. Here we cannot do this."

According to Kernel docs Documentation/Configure.help: "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 swapon -s.

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 (doesn't seem suitable for mobile machines).

7. read the sig11 FAQ .

8. disable the cache from your BIOS settings.

9. install a fan for the video card or exchange video RAM (doesn't seem suitable for mobile machines).

10. install a better fan for the CPU (doesn't seem suitable for mobile machines).

11. exchange RAM chips (doesn't seem suitable for mobile machines).

12. exchange the motherboard (doesn't seem suitable for mobile machines).

12.18.5. APM and PCMCIA

From the PCMCIA-HOWTO: "Card Services can be compiled with support for APM (Advanced Power Management) if you've configured your kernel with APM support. ... The PCMCIA modules will automatically be configured for APM if a compatible version is detected on your system. Whether or not APM is configured, you can use cardctl suspend before suspending your laptop, and cardctl resume after resuming, to cleanly shut down and restart your PCMCIA cards. This will not work with a modem that is in use, because the serial driver isn't able to save and restore the modem operating parameters. APM seems to be unstable on some systems. If you experience trouble with APM and PCMCIA on your system, try to narrow down the problem to one package or the other before reporting a bug. Some drivers, notably the PCMCIA SCSI drivers, cannot recover from a suspend/resume cycle. When using a PCMCIA SCSI card, always use cardctl eject prior to suspending the system.".

12.18.6. APM and Resuming X Windows

Some machines have APM firmware that fails to save and restore display controller chip registers across a suspend. Earlier versions of the XFree86 X server did not restore the screen properly after resume, a problem which was addressed by Linux Laptops. However, contemporary versions of XFree86 mostly do the right thing.

Sometimes X and APM don't work smoothly together. The machine might even hang. A recommendation from Steve Rader: Some linux systems have their X11 server hang when doing apm -s. Folks with this affliction might want to switch to the console virtual terminal and then suspend chvt 1; apm -s as root, or, more appropiately sudo chvt 1; sudo apm -s. I have these commands in a script, say, my-suspend and then do xapmload --click-command my-suspend .

12.18.7. Software Suspend

Software suspend enables the possibility of suspending a machine. It doesn't need APM. You may suspend your machine by either pressing Sysrq-d or with swsusp or shutdown -z (patch for sysvinit needed). It creates an image which is saved in your active swaps. By the next booting the kernel detects the saved image, restores the memory from it and then it continues to run as before you've suspended. If you don't want the previous state to continue use the noresume kernel option.

Software suspends may even be better than hibernate, because now I can suspend my Linux system, boot into Microsoft Windows, perform a few illegal operations and be shut down, and then restart my Linux setup exactly where I left off! This is something that cannot be done with hibernation, since that always restores the last state that you suspended from, be it Microsoft Windows or Linux. So if I want to switch to Microsoft Windows to play games or do anything else, I can leave my Linux desktop exactly as it is and return to how I left it.

In recent 2.6 kernels SoftWareSuspend is part of the kernel. You may find it in the section Power Management. But there are also backports to 2.4 available.

Since the original Software Suspend code was written by Gabor Kuti and Pavel Machek back in 1998, three different implementations have been created for the 2.6 kernel, all forks of the same original codebase. Here is a quick comparison between the two that still exist.

Software Suspend 2 has a long feature list, including the ability to cancel a suspend by pressing Escape, image compression to save time and space, a versatile plugin architecture, and support for machines with Highmem, preemption and SMP.

12.18.8. Tips and Tricks

 export PS1="\$(cat /proc/apm | awk '{print \$7}') \h:\w\$ "

 # Color the bash prompt in function of the percentage of battery
# with acpi subsystem.
# Based on the originally apm based script that has been posted
# on debian-laptop by 
# Jason Kraftcheck <kraftche at cae.wisc.edu>.
#
# This script is licensed under the GNU GPL version 2 or later,
# see /usr/share/common-licences/GPL on a Debian system or
# http://www.gnu.org/copyleft/gpl.html on the web.
 
# (c) 2003 Fabio 'farnis' Sirna <farnis at libero dot it>

function acpi_percent()
{
 if [ `cat /proc/acpi/battery/BAT0/state | grep present: |cut -d\  -f18` = "yes" ]; then
  {
   CAPACITY=`cat /proc/acpi/battery/BAT0/info |grep "design capacity:"|cut -d\  -f11`
   LEVEL=`cat /proc/acpi/battery/BAT0/state | grep remaining|cut -d\  -f8`
   ACPI_PERCENT=`echo $(( $LEVEL * 100 / $CAPACITY ))`
   if [ "$LEVEL" = "$CAPACITY" ]; then
    echo FULL
   else
    echo $ACPI_PERCENT%
   fi
  }
 else echo "NO BATTERY"
 fi
}

function acpi_charge()
{
 ACPI_CHARGE=`cat /proc/acpi/ac_adapter/AC/state | cut -d\  -f20`
 case $ACPI_CHARGE in
       *on-line*)
         ACPI_CHARGE="+" ;;
       *off-line*)
         ACPI_CHARGE="-" ;;
     esac
     echo $ACPI_CHARGE
}

function acpi_color()
   {
     if  [  "$(acpi_charge)"  =  "+"  ];  then
      {
       if [ `cat /proc/acpi/battery/BAT0/state | grep present: |cut -d\  -f18` = "no" ]; then
        echo  "0;31"
       else echo  "1;32"
      fi
     }
     else
       case  $(acpi_percent)  in
          10?%)  echo  "0;32"  ;;
           9?%)  echo  "0;32"  ;;
           8?%)  echo  "0;32"  ;;
           7?%)  echo  "0;32"  ;;
           6?%)  echo  "0;32"  ;;
           5?%)  echo  "0;32"  ;;
           4?%)  echo  "0;33"  ;;
           3?%)  echo  "0;33"  ;;
           2?%)  echo  "0;33"  ;;
           1?%)  echo  "0;31"  ;;
            ?%)  echo  "0;31;5"  ;;
             *)  echo  "0;35"  ;;

       esac
     fi
   }

function  acpi_color_prompt
   {
     PS1='\[\e[$(acpi_color)m\][$(acpi_charge)$(acpi_percent)][\t] \u:\w\$>\[\e[0;37m\] '
   }

   #  linux  console
   if  [  "$TERM"  =  "linux"  ];  then
     PROMPT_COMMAND=acpi_color_prompt
   fi

   function  echo_acpi
   {
     echo -n "($(acpi_charge)$(acpi_percent)) "
   }

 append="apm=on"

 append="acpi=off apm=on"