adjtime(5) — Linux manual page


ADJTIME_CONFIG(5)               File Formats               ADJTIME_CONFIG(5)

NAME         top

       adjtime - information about hardware clock setting and drift factor

SYNOPSIS         top


DESCRIPTION         top

       The file /etc/adjtime contains descriptive information about the
       hardware mode clock setting and clock drift factor.  The file is read
       and write by hwclock; and read by programs like rtcwake to get RTC
       time mode.

       The file is usually located in /etc, but tools like hwclock(8) or
       rtcwake(8) can use alternative location by command line options if
       write access to /etc is unwanted.  The default clock mode is "UTC" if
       the file is missing.

       The Hardware Clock is usually not very accurate.  However, much of
       its inaccuracy is completely predictable - it gains or loses the same
       amount of time every day.  This is called systematic drift.  The util
       hwclock keeps the file /etc/adjtime, that keeps some historical
       information.  For more details see "The Adjust Function" and  "The
       Adjtime File" sections from hwclock(8) man page.

       The format of the adjtime file is, in ASCII.

   First line
       Three numbers, separated by blanks:

       drift factor
              the systematic drift rate in seconds per day (floating point

       last adjust time
              the resulting number of seconds since  1969  UTC  of  most
              recent adjustment or calibration (decimal integer)

       adjustment status
              zero (for compatibility with clock(8)) as a floating point

   Second line
       last calibration time
              The resulting number of seconds since 1969 UTC of most recent
              calibration.  Zero if there has been no calibration yet or it
              is known that any previous calibration is moot (for example,
              because the Hardware Clock has been found, since that
              calibration, not to contain a valid time).  This is a decimal

   Third line
       clock mode
              Supported values are "UTC" or "LOCAL".  Tells whether the
              Hardware Clock is set to Coordinated Universal Time or local
              time.  You can always override this value with options on the
              hwclock command line.

FILES         top


SEE ALSO         top

       hwclock(8), rtcwake(8)

AVAILABILITY         top

       This man page is part of the util-linux package and is available from

COLOPHON         top

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util-linux                       August 2018               ADJTIME_CONFIG(5)