apmd - Advanced Power Management (APM) daemon
apmd [ -c check_seconds ] [ -P proxy_cmd ] [ -p per- cent_to_log ] [ -qVvW ] [ -w warn_percent ] [ -? ] [depre- cated 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 avail- able 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 pend- ing 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 (indicat- ing 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 sys- tem-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 parame-
ter 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 sev- eral days. ("Hibernation is a kind of super-sus- pend, 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 hiberna- tion.) 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 imme- diately 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 hard- ware clock; this will normally have been handled by the kernel's APM driver. PCMCIA devices may need to be manually resumed from standby using card*- ctl(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. Other-
wise, 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 intelli- gent 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.
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 pro- vided, they take precedence over any proxy command invoca- tion for each event.
The first status report printed after a power change may be inaccurate because the power change occured at a frac- tional 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 dra- matically over-estimated.
There needs to be a more general hook to let other appli- cations 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 Pen-
narun (apenwarr@worldvisions.ca).
apm(1) , xapm(1) , cardctl(8) , hdparm(8) , syslogd(8)