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Apart from these processes, journaling file systems, like ReiserFS and Ext3, write their
metadata independently from bdflush, which also prevents the hard disk from spinning
down. To avoid this, a special kernel extension has been developed for mobile devices.
See /usr/src/linux/Documentation/laptop-mode.txt for details.
Another important factor is the way active programs behave. For example, good editors
regularly write hidden backups of the currently modified file to the hard disk, causing
the disk to wake up. Features like this can be disabled at the expense of data integrity.
In this connection, the mail daemon postfix makes use of the variable
POSTFIX_LAPTOP. If this variable is set to yes, postfix accesses the hard disk far
less frequently. However, this is irrelevant if the interval for kupdated was increased.
29.5 The powersave Package
The powersave package cares about all the previously-mentioned power saving
functions. Due to the increasing demand for lower energy consumption in general, some
of its features are also importand on workstations and servers, such as suspend, standby,
or cpu frequency scaling.
This package contains all power management features of your computer. It supports
hardware using ACPI, APM, IDE hard disks, and PowerNow! or SpeedStep technologies.
The functionalities from the packages apmd, acpid, ospmd, and cpufreqd (now
cpuspeed) have been consolidated in the powersave package. Daemons from these
packages, except acpid that acts as a multiplexer for acpi events, should not be run
concurrently with the powersave daemon.
Even if your system does not contain all the hardware elements listed above, use the
powersave daemon for controlling the power saving function. Because ACPI and APM
are mutually exclusive, you can only use one of these systems on your computer. The
daemon automatically detects any changes in the hardware configuration.
29.5.1 Configuring the powersave Package
The configuration of powersave is distributed to several files. Every configuration option
listed there contains additional documentation about its functionality.
Power Management
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Troubleshooting
