Power Management - Ubuntu

There are two methods of power management for your laptop; ACPI and APM. APM or Advanced Power Management is the older of the two and works with the BIOS of the computer.

The disadvantage of APM is that the BIOS functions and manages the power without any real understanding of the operating system. The advantage is that it is well supported by Linux distros. The APM daemon consists of three programs:

apmd – controls power management tasks
apm – command line access to print current battery status or suspend power
xapm – battery meter for X Window

The location of the apmd daemon is /etc/init.d/apmd.

Advanced Configuration and Power Interface (ACPI)
ACPI provides the interface on both workstations and servers to shutdown automatically when requested. It is also used by power management to extend battery life by working with the operating system as well as the BIOS. This provides greater flexibility for responding to power events which may be initiated by the operating system or user.

You are able to see the version that you are running with this command:
cat /proc/acpi/info
version: 20060707

Since Microsoft was the first vendor to implement ACPI, many BIOSs are configured to meet Microsoft ACPI standards but may not be as effective when the computer has Linux installed on it.

In the example below you see the command to view the current status of the battery, temperature and also to determine if the AC Adapter is connected.

acpi -V
Battery 1: charged, 100%
Thermal 1: ok, 75.0 degrees C
AC Adapter 1: on-line

If you consistently have problems with ACPI you can deactivate ACPI support with the acpi=off command to the kernel during the boot process.

Gnome Power Management
This graphical interface to managing power is available from System-Preferences and Power Management

You have 3 tabs, the first is “Running on AC”. The settings for when you are using the power supply are available in this tab.

Sleep allows you to put the machine into a sleep mode after a set period of time. Note that there is a setting for Sleep on the display and Sleep for the whole system.

Understanding Suspend and Hibernate
It is important when making choices that you understand the difference between suspend and hibernate. Both are power saving options that you may choose.

Suspend
This is the lowest possible usage of power savings. It will maintain your data that may be in RAM memory, or maintain the Writer document that you had open. However, in suspend the computer will not complete any calculations or any other actions. The computer will remain in suspend until a key is used to activate the computer. Even once the key is pressed it may take a few seconds before the computer can activate.

Hibernate
Hibernate will save the computer state to the hard disk and then turn off the power. It looks to the user that the computer is off but it actually is running. This is a power sleep state not a power saving state like suspend. If the battery actually ran out of power in this state the user would not loose any information as it had been saved to disk. The computer can be activated with a key selection which may take as long as a minute before the computer can come out of hibernation.

Actions refer to what should happen when the lid on the laptop is closed. The options include Blank Screen, Suspend and Hibernate. The choice you make is actually determined by the length of time before you expect to return.

More important for power management is when the laptop is running on battery. Typically it is important to conserve on system usage to lengthen the time you are able to run on battery. Again, you may set Sleep times for the display and the machine. The same options for what to do when the lid is closed are available. When the battery is closed to shutting off you have the option to Shutdown, Suspend, Hibernate or Do Nothing. It makes sense to Shutdown as the other options may only cause trouble.

The General Tab provides additional information for Power Management including setting the Sleep type, Do nothing, Suspend, or Hibernate and what to do when the power button is pressed: Ask me, Do nothing, Suspend, or Hibernate.

The Notification Area refers to the icon on the Panel. The example shows the green icon indicating that the battery is fully charged.

This example shows the icon on the panel. When you hold the mouse over it you get the status.

Here are several options that are available once you right click the icon on the Panel.