chronyd man page on Oracle

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CHRONYD(8)		     System Administration		    CHRONYD(8)

       chronyd - chrony background daemon

       chronyd [OPTIONS]

       chrony  is  a pair of programs for maintaining the accuracy of computer
       clocks. chronyd is a background daemon program that can be  started  at
       boot time.

       chronyd is a daemon which runs in background on the system.  It obtains
       measurements (e.g. via the network) of the system's offset relative  to
       other  systems,	and adjusts the system time accordingly.  For isolated
       systems, the user can periodically  enter  the  correct	time  by  hand
       (using  chronyc).  In either case, chronyd determines the rate at which
       the computer gains or loses time, and compensates for this.

       chronyd is usually started at boot-time and requires  superuser	privi‐

       If    chronyd	has   been   installed	 to   its   default   location
       /usr/sbin/chronyd, starting it is simply a matter of entering the  com‐


       Information messages and warnings will be logged to syslog.

       A summary of the options supported by chronyd is included below.

       -P priority
	      This  option  will  select the SCHED_FIFO real-time scheduler at
	      the specified priority (which must be between 0 and 100).	  This
	      mode is supported only on Linux.

       -m     This  option will lock chronyd into RAM so that it will never be
	      paged out.  This mode is only supported on Linux.

       -n     When run in this mode, the program will not detach  itself  from
	      the terminal.

       -d     When  run	 in this mode, the program will not detach itself from
	      the terminal, and all messages will  be  sent  to	 the  terminal
	      instead of to syslog.

       -f conf-file
	      This option can be used to specify an alternate location for the
	      configuration file (default /etc/chrony.conf).

       -r     This option will reload sample histories for each of the servers
	      being  used.  These histories are created by using the dump com‐
	      mand in chronyc, or by setting the dumponexit directive  in  the
	      configuration  file.   This option is useful if you want to stop
	      and restart chronyd briefly for any reason, e.g.	to  install  a
	      new  version.  However, it only makes sense on systems where the
	      kernel  can  maintain  clock  compensation  whilst   not	 under
	      chronyd's	 control.   The only version where this happens so far
	      is Linux.	 On systems where this is not the case,	 e.g.  Solaris
	      and SunOS the option should not be used.

       -R     When  this  option  is  used, the initstepslew directive and the
	      makestep directive used with a positive limit will  be  ignored.
	      This option is useful when restarting chronyd and can be used in
	      conjuction with the -r option.

       -s     This option will set the system clock from the computer's	 real-
	      time  clock.   This is analogous to supplying the -s flag to the
	      /sbin/clock program during the Linux boot sequence.

	      Support for real-time clocks is limited at present - the	crite‐
	      ria are described in the section on the rtcfile directive in the
	      documentation supplied with the distribution.

	      If chronyd cannot support the real time clock on your  computer,
	      this  option cannot be used and a warning message will be logged
	      to the syslog.

	      If used in conjunction with the -r flag, chronyd will attempt to
	      preserve the old samples after setting the system clock from the
	      real time clock.	This can be used to allow chronyd  to  perform
	      long  term  averaging  of	 the  gain  or loss rate across system
	      reboots, and is useful for dial-up systems that  are  shut  down
	      when  not	 in  use.  For this to work well, it relies on chronyd
	      having been able to determine accurate statistics for  the  dif‐
	      ference  between	the real time clock and system clock last time
	      the computer was on.

       -u user
	      When this option is used, chronyd will drop root	privileges  to
	      the  specified  user.   So far, it works only on Linux when com‐
	      piled with capabilities support.

       -v     This option displays chronyd's version number  to	 the  terminal
	      and exits

       -4     Resolve  hostnames  only	to IPv4 addresses and create only IPv4

       -6     Resolve hostnames only to IPv6 addresses and  create  only  IPv6


       To report bugs, please visit

       chronyd	is documented in detail in the documentation supplied with the
       distribution (chrony.txt and chrony.texi) and is	 also  available  from

       chrony(1), chronyc(1), chrony.conf(5), hwclock(8), ntpd(8)

       Richard Curnow <>

       This man-page was written by Jan Schaumann <> as
       part of "The Missing Man Pages Project".	  Please  see‐ for details.

       The complete chrony documentation is supplied in texinfo format.

chrony 1.29.1			 January 2014			    CHRONYD(8)

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