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28.3 ACPI
ACPI (advanced configuration and power interface) was designed to enable the operating
system to set up and control the individual hardware components. ACPI supersedes
both PnP and APM. It delivers information about the battery, AC adapter, temperature,
fan, and system events, like "close lid" or "battery low."
The BIOS provides tables containing information about the individual components and
hardware access methods. The operating system uses this information for tasks like
assigning interrupts or activating and deactivating components. Because the operating
system executes commands stored in the BIOS, the functionality depends on the BIOS
implementation. The tables ACPI can detect and load are reported in /var/log/boot
.msg. See
Section 28.3.4, "Troubleshooting"
(page 512) for more information about
troubleshooting ACPI problems.
28.3.1 ACPI in Action
If the kernel detects an ACPI BIOS when the system is booted, ACPI is activated auto-
matically and APM is deactivated. The boot parameter acpi=force may be necessary
for some older machines. The computer must support ACPI 2.0 or later. Check the
kernel boot messages in /var/log/boot.msg to see if ACPI was activated.
Subsequently, a number of modules must be loaded. This is done by the start script of
acpid. If any of these modules cause problems, the respective module can be excluded
from loading or unloading in /etc/sysconfig/powersave/common. The system
log (/var/log/messages) contains the messages of the modules, enabling you to
see which components were detected.
/proc/acpi now contains a number of files that provide information about the system
state or can be used to change some of the states. Some features do not work yet because
they are still under development and the support of some functions largely depends on
the implementation of the manufacturer.
All files (except dsdt and fadt) can be read with cat. In some files, settings can be
modified with echo, for example, echo X > file to specify suitable values for
X. One possibility for easy access to those values is the powersave command, which
acts as a front-end for the Powersave daemon. The following describes the most impor-
tant files:
Power Management
507
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Table of Contents
Troubleshooting
