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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 nor-mally normally
     mally 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 system while using an external
     power source, and specified independently for operation using internal batteries.  By default, the val-ues values
     ues 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