Power Management

Configuring Hardware - Power Management

If you have a laptop, you will probably want to make a few measures to extend your battery life, such as throttling down your CPU, dimming your LCD backlight, and other things. In this case you will want to make sure the laptop USE flag is set in your /etc/make.conf. If you have a dell laptop, you will also want to add the dell USE flag. Chances are you have already built some of the packages that accept these USE flags, so you may want to rebuild all affected packages on your system.

$ sudo emerge -avDN world

If it hasn't been installed already, you'll want to install the acpi (Advanced Configuration and Power Interface) daemon.

$ sudo emerge -av apcid

Once the package is emerged, we'll start the apci daemon and add it to startup.

$ sudo /etc/init.d/acpid start
$ sudo rc-update add acpid default

The next we'll create a "battery" runlevel for your system.

$ cd /etc/runlevels
$ sudo cp -a default battery

This action creates a copy of the default runlevel called battery. From now on, whenever you add a service to the default runlevel, if you want it to start up when you are running only on your battery, you will need to add it to the battery runlevel as well. The next step will be to create a script that can intercept from the acpid whether or not your system is running on batteries and be able to switch to the appropriate runlevel. This script was blatantly stolen from the gentoo handbook.

$ sudo mkdir /etc/acpi/actions
$ sudo nano -w /etc/acpi/actions/pmg_switch_runlevel.sh

/etc/acpi/actions/pmg_switch_runlevel.sh

#!/bin/bash

# BEGIN configuration
RUNLEVEL_AC="default"
RUNLEVEL_BATTERY="battery"
# END configuration

if [ ! -d "/etc/runlevels/${RUNLEVEL_AC}" ]
then
    logger "${0}: Runlevel ${RUNLEVEL_AC} does not exist. Aborting."
    exit 1
fi

if [ ! -d "/etc/runlevels/${RUNLEVEL_BATTERY}" ]
then
    logger "${0}: Runlevel ${RUNLEVEL_BATTERY} does not exist. Aborting."
    exit 1
fi

if on_ac_power
then
    if [[ "$(</var/lib/init.d/softlevel)" != "${RUNLEVEL_AC}" ]]
    then
        logger "Switching to ${RUNLEVEL_AC} runlevel"
         /sbin/rc ${RUNLEVEL_AC}
    fi
elif [[ "$(</var/lib/init.d/softlevel)" != "${RUNLEVEL_BATTERY}" ]]
then
    logger "Switching to ${RUNLEVEL_BATTERY} runlevel"
    /sbin/rc ${RUNLEVEL_BATTERY}
fi

We'll also need to make this script executable.

$ chmod 755 /etc/acpi/actions/pmg_switch_runlevel.sh

Next we will need to determine what events are thrown when you unplug or plug in your AC adapter.

$ sudo tail -f /var/log/messages | grep "ACPI event"

You should see something like this:

Dec  7 18:10:30 moonbase3 logger: ACPI event unhandled: ac_adapter AC0 00000080 00000000
Dec  7 18:10:30 moonbase3 logger: ACPI event unhandled: processor CPU0 00000081 00000000
Dec  7 18:10:31 moonbase3 logger: ACPI event unhandled: processor CPU1 00000081 00000000
Dec  7 18:10:31 moonbase3 logger: ACPI event unhandled: processor CPU2 00000081 00000000
Dec  7 18:10:31 moonbase3 logger: ACPI event unhandled: processor CPU3 00000081 00000000
Dec  7 18:10:31 moonbase3 logger: ACPI event unhandled: battery BAT0 00000080 00000001
Dec  7 18:10:33 moonbase3 logger: ACPI event unhandled: ac_adapter AC0 00000080 00000001
Dec  7 18:10:33 moonbase3 logger: ACPI event unhandled: processor CPU0 00000081 00000000
Dec  7 18:10:33 moonbase3 logger: ACPI event unhandled: processor CPU1 00000081 00000000
Dec  7 18:10:33 moonbase3 logger: ACPI event unhandled: processor CPU2 00000081 00000000
Dec  7 18:10:34 moonbase3 logger: ACPI event unhandled: processor CPU3 00000081 00000000
Dec  7 18:10:34 moonbase3 logger: ACPI event unhandled: battery BAT0 00000080 00000001

What we're interested in is the info for the AC adapter and battery. We can see in the output above that events for the AC adapter are called ac_adapter, and battery events are called, well, battery. We'll create two files in /etc/acpi/actions/ to intercept the events.

$ sudo nano -w /etc/acpi/actions/pmg_ac_adapter

Add the following from the gentoo handbook:

# replace "ac_adapter" below with the event generated on your laptop
# For example, ac_adapter.* will match ac_adapter AC 00000080 00000000
event=ac_adapter.*
action=/etc/acpi/actions/pmg_switch_runlevel.sh %e

Do the same for the battery.

$ sudo nano -w /etc/acpi/actions/pmg_battery

Add the following from the gentoo handbook:

# replace "battery" below with the event generated on your laptop
# For example, battery.* will match battery BAT0 00000080 00000001
event=battery.*
action=/etc/acpi/actions/pmg_switch_runlevel.sh %e

We'll need to restart the daemon for the changes to take effect.