Advanced Power Management (APM) daemon. It is used for the UPS to shutdown computer when the power fails.
It is mostly found in modern laptop computers and most modern desktops.
Now lets see the manual of apmd service.Manual apmd:NAME
apmd - Advanced Power Management (APM) daemonSYNOPSIS
apmd [ -c check_seconds ] [ -P proxy_cmd ] [ -p percent_to_log ] [ -qVvW ] [ -w warn_percent ] [ -? ] [deprecated
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
either specified using the -P option, or /etc/apm/apmd_proxy by default. It 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
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 drivers may be
in a confused state.
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.
The APM driver has reported that the BIOS thinks the strength of one (or more) batteries is 'low'; at least
ten minutes of power should remain.
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.OPTIONS
-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
-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.
Print the daemon's version and exit.
Enables verbose mode, where each event reported by the APM driver is logged.
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
-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.
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.)
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
-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.
(This option is now completely ignored. Edit apmd_proxy instead.) This means 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.BUGS
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
Multiple batteries are currently treated as if they were just one large one.FILES
This program was written by Rik Faith (email@example.com) 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
apm(1), xapm(1), cardctl(8), hdparm(8), syslogd(8)