PACEMAKER(8) BSD System Manager's Manual PACEMAKER(8)NAMEpacemaker — clock drift adjustment daemon
SYNOPSISpacemaker [-d drift] [-b] [-e error] [-a interval] [-i] [-v] [-n]
DESCRIPTIONpacemaker 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 ALSOlaunchd(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
