APMD

apmd ? Advanced Power Management (APM) daemon

apmd [ ?c check_seconds ] [ ?P proxy_cmd ] [ ?p percent_to_log ] [ ?qVvW ] [ ?w warn_percent ] [ ?? ] [deprecated options]

apmd is an APM monitoring daemon, and works in conjunction with the APM BIOS driver in the OS kernel. It can execute a command (normally a shell script) when certain events are reported by the driver, and will log, via syslogd(8), certain changes in system power status. When the available battery power becomes very low, it can alert all users on the system using several methods.

When the kernel APM driver notifies the daemon of a pending suspend or standby request, apmd will invoke the approprate command, log the event, sync(2) data to the disk, sleep briefly to help ensure all the data actually gets to the disk, and then tell the APM driver to continue its operation. However, for "critical" suspends (indicating an emergency shutdown) only the last step (telling the driver to continue) is performed.

Most uses of this daemon will use the proxy command to support power conservation activities. This command is searched for by default in /etc/apmd_proxy and is invoked with one or two arguments:

start

Invoked when the daemon starts. Normally sets system-wide power policy, such as IDE hard drive standby times, to account for whether battery power is in use.

stop

Invoked when the daemon stops. Normally undoes any policy settings done when the daemon started.

suspend [ system | user ]

Invoked when the APM driver reports that system suspension has been initiated. The second parameter indicates whether the BIOS or a user action (such as closing a laptop) initiated suspension.

The BIOS "suspend" mode aggressively conserves power, and normally involves shutting off power to all devices except the CPU core and memory, which is kept in a very low power mode. Most laptops can stay suspended, using battery power alone, for several days. ("Hibernation" is a kind of super-suspend, where all that state is written to disk and the machine uses even less power bcause it can turn off that CPU core, using no battery power at all. At this writing, Linux does not support hibernation.) PCMCIA devices should be manually suspended using cardctl(8), and some modular drivers may need to be unloaded.

standby [ system | user ]

Invoked when the APM driver reports that system standby has been initiated. The second parameter indicates whether the BIOS or a user action (such as invoking apm -s) caused this.

The BIOS "standby" mode slightly conserves power, and leaves the machine able to respond almost immediately to user activity. Most laptops can’t stay in standby mode for even a day, if they must rely on battery power. Normally, nothing needs to be done beyond what the BIOS itself will do.

resume [ suspend | standby | critical ]

Invoked when the APM driver reports that system has resumed normal operation. The second parameter indicates what sort of mode it was in before, either the "suspend" mode (possibly a "critical" suspend) or else "standby" mode.

The system clock must be updated to match the hardware clock; this will normally have been handled by the kernel’s APM driver. PCMCIA devices may need to be manually resumed from standby using cardctl(8), and some modular drivers may need to be reloaded or otherwise reinitialized. In the case of a critical suspend, system state may not have been completely saved due to an emergency shutdown; applications and and drivers may be in a confused state.

change power

This presents a subset of the APM driver "power change" events, specifically those where AC power was added or removed. This will often modify the system wide power policy; for example, so that IDE hard drives aggressively enter standby mode when only battery power is available.

change battery

The APM driver has reported that the BIOS thinks the strength of one (or more) batteries is "low"; at least ten minutes of should power remain.

change capability

Some change in the power management capabilities of the system was reported. It may have been caused by operation of some setup utility, or by the arrival or removal of some devices.

This daemon issues a number of different log messages, most of which should be self explanatory. The messages emitted for battery status need some explanation, however. The information logged contains 4 fields after a "Battery" or "Charge" label:

1) Rate of discharge (percent/minute). Negative rates indicate charging.

2) Time since total charge or total discharge (hh:mm:ss). This value is only useful if it reflects the time since a 100% or 0% state has been reached. Otherwise, this time is in parentheses, and reflects the time since the last "important" apmd status change such as starting the daemon, changing from AC power to battery power, and so on.

3) Estimate of time left until total discharge (or total charge), assuming use similar to that since the last resume ( or since AC was connected). This time is calculated by apmd itself.

4) Parenthetically, the percent and length of remaining battery life, as estimated by the APM BIOS (which is often a conservative estimate from an intelligent battery itself). This particular information is provided with most messages from this daemon.

This daemon supports APM BIOS 1.2 events, though it does not support some of the advanced features such as multiple batteries. Also, there is no interaction yet with ACPI support as found in newer PC hardware.

?c seconds, ?-check seconds

Controls how many seconds to block on the /dev/apm_bios device. Normally the daemon blocks until the APM driver reports an event; this number may be changed to cause battery charge or discharge rates to be checked more often.

?P proxy_cmd, ??apmd_proxy proxy_cmd

Identifies the command to invoke when certain APM driver events are reported. See above for information about the arguments to this script.

?p percent_change, ?-percentage percent_change

Every time the percentage of available power changes (discharge or recharge) by percent_change, log information. The default is 5. Use values greater than 100 to disable this feature.

?V, ??version

Print the daemon’s version and exit.

?v, ??verbose

Enables verbose mode, where each event reported by the APM driver is logged.

?W, ??wall

In addition to logging low battery status (as determined either by the -w level or by the APM BIOS) using syslog(2), also use wall(1) to alert all users. This is most useful if syslogd(8) is not set up to write ALERT messages to all users. If both methods are used, more warnings will be made during the critical time period.

?w warn_percent, ?-warn warn_percent

When the battery is not being charged and the percentage of available power drops below warn_percent, log a warning at ALERT level to syslog(2). If the ?W or ??wall flag was given, the daemon will also use wall(1) to alert all users of impending doom. Give the warning each time the percentage changes. The default is 10. Use negative values to disable this feature.

?q, ??quiet

Disables the warnings identified by the -W and -w options. (The APM BIOS on many machines will provide an audible warning when power is about to be used up, so those extra warnings may not be needed.)

??, ??help

Prints a usage message and exits.

New software should only use the proxy script, rather than the following now-deprecated options (most of which have never appeared in a production release). If they are provided, they take precedence over any proxy command invocation for each event.

?a ac_online_cmd, ??ac_online ac_online_cmd

Provides a command to be run when AC power becomes available, though not when the daemon first starts.

?b ac_offline_cmd, ??ac_offline ac_offline_cmd

Provides a command to be run when the machine is operating on battery power, though not when the daemon first starts.

?l low_battery_cmd, ??low_battery low_battery_cmd

Provides a command to be run when the APM BIOS judges that battery power is "low".

?s pre_suspend_cmd, ??pre_suspend pre_suspend_cmd

Provides a command to be run before suspending through the driver.

?r post_resume_cmd, ??post_resume post_resume_cmd

Provides a command to be run after resuming through the driver.

?u, ??utc

(This option is now completely ignored.) The BIOS clock is set to UTC (GMT), so the daemon should pass the -u option to the clock or hwclock program when coming out of suspend or resume mode, or when responding to the BIOS update time event.

The first status report printed after a power change may be inaccurate because the power change occured at a fractional percentage that was rounded to a full percentage. For example, say you are discharging the machine and have 50.9% power, which is reported as 50%. When you start to charge the machine, it will only have 0.1% left before the percentage flips to 51%, and the charge rate will be dramatically over-estimated.

There needs to be a more general hook to let other applications participate in system power management decisions and policies.

Multiple batteries are currently treated as if they were just one large one.

/dev/apm_bios
/proc/apm
/etc/apmd/apmd_proxy

This program was written by Rik Faith (faith@cs.unc.edu) and may be freely distributed under the terms of the GNU General Public License. There is ABSOLUTELY NO WARRANTY for this program. The current maintainer is Avery Pennarun (apenwarr@worldvisions.ca).

apm(1), xapm(1), cardctl(8), hdparm(8), syslogd(8)