APMD(8)                    Linux Programmer's Manual                   APMD(8)

       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 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

              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 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 power
              should 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

       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

       -?, --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

       -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.  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.

       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-

       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


       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)

                                  10 Jun 1999                          APMD(8)