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pacemaker(8)              BSD System Manager's Manual             pacemaker(8)


NAME

     pacemaker -- clock drift adjustment daemon


SYNOPSIS

     pacemaker [-d drift] [-b] [-e error] [-a interval] [-i] [-v] [-n]


DESCRIPTION

     pacemaker adjusts the system clock periodically to compensate for clock
     drift.  The clock drift is normally computed by ntpd(8), which writes a
     clock drift value in /var/db/ntp.drift.  By default, pacemaker will call
     adjtime(2) once per second to slew the system clock.  The daemon is
     started by launchd(8) only when the drift file is present or has just
     been created in the file system.  pacemaker detects changes in the file
     and re-calculates clock adjustment values appropriately.  The daemon will
     exit if the drift file is deleted and is not re-created within one
     minute.

     As a fail-safe mechanism, pacemaker will reset the system clock using
     settimeofday(2) if the system clock requires adjustment exceeding the
     maximum value that can be accomodated by adjtime to slew the clock.  In
     practice, this extreme case should never occur.

     The -d option allows the specification of either a floating-point drift
     value, or the path name of an alternate drift file.  If a floating point
     drift value is specified, pacemaker will use the given value and will not
     read a drift file.

     To reduce power consumption, especially when the system is using internal
     battery power, it may be desirable to reduce the frequency of calls to
     adjust the system's clock drift.  The -e and -a options, together with
     the -b flag allow several ways to control the clock adjustment frequency.

     The floating point value following -e specifies a maximum error tolerance
     in seconds for the system clock.  For example, a value of 0.001 specifies
     that the clock drift adjustment should only be done frequently enough to
     keep the system clock error within one millisecond, based on the current
     clock drift rate.

     Alternatively, the clock adjustment frequency can be specified exactly as
     a value in seconds following -a.

     When both -e error and -a interval are provided, pacemaker will choose to
     adjust the system clock either every interval seconds, or less frequently
     if the clock error will remain within error seconds.

     The settings for -e and/or -a may be specified for operation of the sys-
     tem while using an external power source, and specified independently for
     operation using internal batteries.  By default, the values for -e and/or
     -a are used for both power configurations.  If the -b flag precedes -e
     and/or -a, then the following settings apply only when the system is
     using internal battery power.

     For example, starting pacemaker with the following parameters will cause
     it to adjust the clock every 2 seconds when the system is using external
     power.  When running on battery power, it will adjust the clock no more
     than once every 10 seconds, or less frequently if the clock error remains
     less than five milliseconds.

           pacemaker -a 2 -b -a 10 -e 0.005

     When invoked on the command-line with -i, pacemaker prints a summary of
     internal parameters and then exits.  The -v flag causes pacemaker to
     print copies of its log messages to standard error.  Note that this
     requires running the program from the command line rather than from
     launchd.  -n causes pacemaker to run without actually attempting to
     adjust the system clock.


FILES

     /var/db/ntp.drift  default clock drift file


SEE ALSO

     launchd(8), ntpd(8), adjtime(2), settimeofday(2).


HISTORY

     The pacemaker daemon was introduced in OS X 10.9.

OS X                             March 9, 2013                            OS X

Mac OS X 10.9 - Generated Fri Oct 18 15:28:53 CDT 2013
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