By default, the sleep modes are inactive, because they still do not work on some computers. There are three basic ACPI sleep modes and two APM sleep modes:

Make sure that the following default options are set in the file /etc/sysconfig/powersave/events for the correct processing of suspend, standby, and resume (default settings following the installation of SUSE Linux):

EVENT_GLOBAL_SUSPEND2DISK=
    "prepare_suspend_to_disk do_suspend_to_disk"
EVENT_GLOBAL_SUSPEND2RAM=
    "prepare_suspend_to_ram do_suspend_to_ram"
EVENT_GLOBAL_STANDBY=
    "prepare_standby do_standby"
EVENT_GLOBAL_RESUME_SUSPEND2DISK=
    "restore_after_suspend_to_disk"
EVENT_GLOBAL_RESUME_SUSPEND2RAM=
    "restore_after_suspend_to_ram"
EVENT_GLOBAL_RESUME_STANDBY=
    "restore_after_standby"

In the file /etc/sysconfig/powersave/battery, define three battery charge levels (in percent) that trigger system alerts or specific actions when they are reached.

BATTERY_WARNING=20
BATTERY_LOW=10
BATTERY_CRITICAL=5

The actions or scripts to execute when the charge levels drop under the specified limits are defined in the configuration file /etc/sysconfig/powersave/events. The standard actions for buttons can be modified as described in Section 21.5.1, “Configuring the powersave Package”.

EVENT_BATTERY_NORMAL="ignore"
EVENT_BATTERY_WARNING="notify"
EVENT_BATTERY_LOW="notify"
EVENT_BATTERY_CRITICAL="wm_shutdown"

The system behavior can be adapted to the type of power supply. The power consumption of the system should be reduced when the system is disconnected from the AC power supply and operated with the battery. Similarly, the performance should automatically increase as soon as the system is connected to the AC power supply. The CPU frequency, the power saving function of IDE, and a number of other parameters can be modified.

The actions to execute when the computer is disconnected from or connected to the AC power supply are defined in /etc/sysconfig/powersave/events. Select the schemes to use in /etc/sysconfig/powersave/common:

AC_SCHEME="performance"
BATTERY_SCHEME="powersave"

The schemes are stored in files in /etc/sysconfig/powersave. The filenames are in the format scheme_name-of-the-scheme. The example refers to two schemes: scheme_performance and scheme_powersave. performance, powersave, presentation, and acoustic are preconfigured. Existing schemes can be edited, created, deleted, or associated with different power supply states with the help of the YaST power management module described in Section 21.6, “The YaST Power Management Module”.

If you experience problems with ACPI, use the command dmesg|grep -i acpi to search the output of dmesg for ACPI-specific messages. A BIOS update may be required to resolve the problem. Go to the home page of your laptop manufacturer, look for an updated BIOS version, and install it. Ask the manufacturer to comply with the latest ACPI specification. If the errors persist after the BIOS update, proceed as follows to replace the faulty DSDT table in your BIOS with an updated DSDT:

Refer to the kernel sources (kernel-source) to see if your processor is supported. You may need a special kernel module or module option to activate CPU frequency control. This information is available in /usr/src/linux/Documentation/cpu-freq/*. If a special module or module option is needed, configure it in the file /etc/sysconfig/powersave/cpufreq by means of the variables CPUFREQD_MODULE and CPUFREQD_MODULE_OPTS.

There are several kernel-related problems that prevent the use of suspend and standby on ACPI systems:

The error may also be due to a faulty DSDT implementation (BIOS). If this is the case, install a new DSDT.

On ACPI and APM systems: When the system tries to unload faulty modules, the system is arrested or the suspend event is not triggered. The same can also happen if you do not unload modules or stop services that prevent a successful suspend. In both cases, try to identify the faulty module that prevented the sleep mode. The log files generated by the powersave daemon in /var/log/suspend2ram.log and /var/log/suspend2disk.log are very helpful in this regard. If the computer does not enter the sleep mode, the cause lies in the last module unloaded. Manipulate the following settings in /etc/sysconfig/powersave/sleep to unload problematic modules prior to a suspend or standby.

UNLOAD_MODULES_BEFORE_SUSPEND2DISK=""
UNLOAD_MODULES_BEFORE_SUSPEND2RAM=""
UNLOAD_MODULES_BEFORE_STANDBY=""
SUSPEND2DISK_RESTART_SERVICES=""
SUSPEND2RAM_RESTART_SERVICES=""
STANDBY_RESTART_SERVICES="" 

If you use suspend or standby in changing network environments or in connection with remotely mounted file systems, such as Samba and NIS, use automounter to mount them or add the respective services, for example, smbfs or nfs, in the above-mentioned variable. If an application accesses the remotely mounted file system prior to a suspend or standby, the service cannot be stopped correctly and the file system cannot be unmounted properly. After resuming the system, the file system may be corrupt and must be remounted.

With ACPI, the operating system can request the BIOS to send a message when the battery charge level drops under a certain limit. The advantage of this method is that the battery state does not need to be polled constantly, which would impair the performance of the computer. However, this notification may not take place when the charge level drops under the specified limit, even though the BIOS supposedly supports this feature. If this happens on your system, set the variable FORCE_BATTERY_POLLING in the file /etc/sysconfig/powersave/battery to yes to force battery polling.