Basic hardware configuration

Advanced Power Management bootstrings

If you need to configure, control, or query the operating system's power management facilities after it has booted, you should use the Power Management control shell, pwrsh(ADM). See ``Configuring Power Management''.

Access to your system's BIOS-APM at boot time by boot(HW) is controlled by the apm.cmd= bootstring. When boot runs, it executes any apm.cmd= lines found in /etc/default/boot (see the boot(F) manual page); these define the default APM handling. Any stand-alone apm.cmd= commands issued at the boot prompt override these settings. Alternatively, apm.cmd= may be specified as an argument to most stand-alone commands.

The following bootstring arguments can be used to configure APM if it is accessible:

apm.boot=test: Only boot if test is true.
apm.check=no: Do not check for APM support. Any BIOS-APM will be ignored.
apm.check=verbose: Same as apm.check=yes, but prints error messages.
apm.check=yes: Check for APM support (default).
apm.exists=disable: Try to disable any BIOS-APM found. The APM is not used again.
apm.exists=ignore: Do not get power status. The BIOS-APM will not be used again.
apm.exists=status: Try to get power status (default). The various internal parameters that store the status of the batteries and mains power can be tested using the apm.warn and apm.boot bootstrings. These allow booting to be aborted and a warning issued if there is insufficient power available.
A status error does not stop APM being used; in that case, the apm.warn= and apm.boot= conditions are not tested.
apm.exists=verbose: Print messages on failure; otherwise, apm.exists=status is silent on errors.
apm.warn=test: Issue a warning if the test is true. The syntax of the boolean test is defined on the hasapm(ADM) manual page.

The apm.warn=test and apm.boot=test strings are used typically to prevent booting when the batteries are exhausted.

The default apm.boot test is:

ac.online | charge.high | charge.low | (!charge.unknown & % >= 15)

which permits the boot process to proceed if AC mains power is being used or the batteries have sufficient charge (greater than or equal to 15%).

The default apm.warn test is:

!ac.online & (charge.low | charge.critical | (!charge.unknown & % <= 25))

which issues a warning if AC mains power is not being used and the BIOS-APM reports that the charge in the batteries is low (less than or equal to 25%).

These tests should work on systems where the APM firmware can deduce the approximate status of the battery without knowing the percentage charge remaining.

On some machines, the APM firmware does not know the condition of the battery. It may then report no charge remaining (% = 0 is true) rather than admitting that the charge is unknown (charge.unknown is true). Consequently, either of the above test conditions may always be true when such machines are using batteries rather than AC power.

To try to overcome this problem, the apm.warn test could be changed to:

!ac.online & !battery.unknown & (charge.critical | % <= 25)

However, this may not work on all such machines.

Different manufacturers interpret different percentages of remaining charge or approximate battery status as being ``high'', ``low'', or ``critical''. These interpretations may have been designed to be used with proprietary software, and so may be misleading. They may not produce satisfactory results if they are used as indicators of the battery's charge state. Checking the percentage of remaining charge should be more satisfactory, but is not possible on all machines.

The kernel can only use APM if it supports a 32-bit Protected Mode interface. If such an interface is available, one of the following bootstrings can be used:

apm.connect=disable: Try to disable BIOS-APM interface. Proceed with boot.
apm.connect=must: Try to connect, and stop booting if this fails.
apm.connect=no: Do not use the BIOS-APM interface. Proceed with boot.
apm.connect=yes: Try to use the BIOS-APM interface, and continue to boot even if this fails (default).

In the absence of such an interface, the following bootstrings are obeyed:

apm.no32pm=disable: Try to disable APM.
apm.no32pm=ignore: Print warning message and proceed to boot. APM will not be used (default).
apm.no32pm=ok: Same as ignore, but no warning is printed.