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adjtimex



SYNOPSIS

       adjtimex [option]...


DESCRIPTION

       This program gives you raw access to the kernel time vari­
       ables.  For a machine connected to the Internet, or
       equipped with a precision oscillator or radio clock, the
       best way to regulate the system clock is with ntpd(8).
       For a standalone or intermittently connected machine, you
       may use adjtimex instead to at least correct for system­
       atic drift.

       Anyone may print out the time variables, but only the
       superuser may change them.

       If your computer can be connected to the net, you might
       run ntpd for at least several hours and use adjtimex
       --print to learn what values of tick and freq it settled
       on.  Alternately, you could estimate values using the CMOS
       clock as a reference (see the --compare and --adjust
       switches).  You could then add a line to rc.local invoking
       adjtimex to set those parameters each time you reboot.


OPTIONS

       Options may be introduced by either - or --, and unique
       abbreviations may be used.  Here is a summary of the
       options, grouped by type.  Explanations follow.

       Get/Set Kernel Time Parameters
              -p --print -t --tick val -f newfreq --frequency
              newfreq -o val --offset val -s adjustment
              --singleshot adjustment -m val --maxerr val -e val
              --esterror val -T val --timeconstant val -a[count]
              --adjust[=count]

       Estimate Systematic Drifts
              -c[count] --compare[=count] -i tim --interval tim
              -l file --logfile file -h timeserver --host
              timeserver -w --watch -r[file] --review[=file] -u
              --utc

       Informative Output
              --help -v --version

       -p, --print
              Print the current values of the kernel time
              variables.  NOTE: The time is "raw", and may be off
              by up to one timer tick (10 msec).  "status" gives
              the value of the time_status variable in the
              kernel.  For Linux 1.0 and 1.2 kernels, the value
              is as follows:
                    0   clock is synchronized (so the kernel should

                   32   deleting leap second
                   64   clock unsynchronized
                  128   holding frequency
                  256   PPS signal present
                  512   PPS signal jitter exceeded
                 1024   PPS signal wander exceeded
                 2048   PPS signal calibration error
                 4096   clock hardware fault

       -t val, --tick val
              Set the number of microseconds that should be added
              to the system time for each kernel tick interrupt.
              There are supposed to be 100 ticks per second, so
              val should be close to 10000.  Increasing val by 1
              speeds up the system clock by about 100 ppm, or
              8.64 sec/day.  tick must be in the range
              9000...11000.

       -f newfreq, --frequency newfreq
              Set the system clock frequency offset to newfreq.
              newfreq can be negative or positive, and gives a
              much finer adjustment than the --tick switch.  The
              value is scaled such that newfreq = 1<<16 speeds up
              the system clock by about 1 ppm, or .0864 sec/day.
              Thus, --tick 10000 --frequency 6553600 is about the
              same as --tick 10001 --frequency 0.  newfreq must
              be in the range -6553600...6553600, allowing
              maximum adjustments of plus or minus 100 ppm.

       -s adj, --singleshot adj
              Slew the system clock by adj usec.  (Its rate is
              changed temporarily by about 1 part in 2000.)

       -o adj, --offset adj
              Add a time offset of adj usec.  The kernel code
              adjusts the time gradually by adj, notes how long
              it has been since the last time offset, and then
              adjusts the frequency offset to correct for the
              apparent drift.  adj must be in the range
              -512000...512000.

       -m val, --maxerror val
              Set maximum error (usec).

       -e val, --esterror val
              Set estimated error (usec).  The maximum and
              estimated error are not used by the kernel.  They
              are merely made available to user processes via the
              adjtimex(2) system call.

       -t val, --timeconstant val
              Set phase locked loop (PLL) time constant.  val
              accuracy.

       -c[count], --compare[=count]
              Periodically compare the system clock with the CMOS
              clock.  After the first two calls, print values for
              tick and frequency offset that would bring the
              system clock into approximate agreement with the
              CMOS clock.  CMOS clock readings are adjusted for
              systematic drift using using the correction in
              /etc/adjtime -- see hwclock(8).  The interval
              between comparisons is 10 seconds, unless changed
              by the --interval switch.  The optional argument is
              the number of comparisons.  (If the argument is
              supplied, the "=" is required.)

       -a[count], --adjust[=count]
              By itself, same as --compare, except the
              recommended values are actually installed after
              every other comparison.  With --review, the tick
              and frequency are set to the least-squares
              estimates.  (In the latter case, any count value is
              ignored.)

       -i tim, --interval tim
              Set the interval in seconds between clock
              comparisons for the --compare and --adjust options.

       -u, --utc
              The CMOS clock is set to UTC (universal time)
              rather than local time.

       -l[file], --log[=file]
              Save the current values of the system and CMOS
              clocks, and optionally a reference time, to file
              (default /var/log/clocks.log).  The reference time
              is taken from a network timeserver (see the --host
              switch) or supplied by the user (see the --watch
              switch).

       -h timeserver, --host timeserver
              Use ntpdate to query the given timeserver for the
              current time.  This will fail if timeserver is not
              running a Network Time Protocol (NTP) server, or if
              that server is not synchronized.  Implies --log.

       -w, --watch
              Ask for a keypress when the user knows the time,
              then ask what that time was, and its approximate
              accuracy.  Implies --log.

       -r[file], --review[=file]
              Review the clock log file (default


EXAMPLES

       If your system clock gained 8 seconds in 24 hours, you
       could set the tick to 9999, and then it would lose 0.64
       seconds a day (that is, 1 tick unit = 8.64 seconds per
       day).  To correct the rest of the error, you could set the
       frequency offset to (1<<16)*0.64/.0864 = 485452.  Thus,
       putting the following in rc.local would approximately
       correct the system clock:

            adjtimex  --tick 9999  --freq 485452


NOTES

       adjtimex adjusts only the system clock -- the one that
       runs while the computer is powered up.  To set or regulate
       the CMOS clock, see hwclock(8).


AUTHORS

       Steven S. Dick <ssd@nevets.oau.org>, Jim Van Zandt
       <jrv@vanzandt.mv.com>.


SEE ALSO

       date(1L), gettimeofday(2), settimeofday(2), hwclock(8),
       ntpdate(8), ntpd(8), /usr/src/linux/include/linux/timex.h,
       /usr/src/linux/include/linux/sched.h,
       /usr/src/linux/kernel/time.c,
       /usr/src/linux/kernel/sched.c

                         October 24, 1998             ADJTIMEX(8)
  




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