chrony man page on Oracle

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CHRONY(1)			 User's Manual			     CHRONY(1)

       chrony - programs for keeping computer clocks accurate

       chronyc [OPTIONS]

       chronyd [OPTIONS]

       chrony  is  a  pair  of	programs for keeping computer clocks accurate.
       chronyd is a background (daemon) program and chronyc is a  command-line
       interface  to it. Time reference sources for chronyd can be RFC1305 NTP
       servers, human (via keyboard and chronyc), or the computer's  real-time
       clock  at  boot	time  (Linux  only). chronyd can determine the rate at
       which the computer gains or loses time and compensate for it  while  no
       external	 reference  is present. Its use of NTP servers can be switched
       on and off (through chronyc) to support computers  with	dial-up/inter‐
       mittent	access to the Internet, and it can also act as an RFC1305-com‐
       patible NTP server.

       chronyc is a command-line interface program which can be used to	 moni‐
       tor  chronyd's  performance  and to change various operating parameters
       whilst it is running.

       chronyd's main function is to obtain measurements  of  the  true	 (UTC)
       time  from one of several sources, and correct the system clock accord‐
       ingly.  It also works out the rate at which the system clock  gains  or
       loses  time  and uses this information to keep it accurate between mea‐
       surements from the reference.

       The reference time can be derived from  either  Network	Time  Protocol
       (NTP)   servers,	 reference  clocks,  or	 wristwatch-and-keyboard  (via
       chronyc).  The main source of information about the Network Time Proto‐
       col is

       It  is designed so that it can work on computers which only have inter‐
       mittent access to reference sources, for example computers which use  a
       dial-up	account to access the Internet or laptops.  Of course, it will
       work well on computers with permanent connections too.

       In addition, on Linux it can monitor the system's real time clock  per‐
       formance, so the system can maintain accurate time even across reboots.

       Typical accuracies available between 2 machines are

       On  an  ethernet	 LAN  :	 100-200  microseconds, often much better On a
       V32bis dial-up modem connection : 10's of milliseconds (from  one  ses‐
       sion to the next)

       With a good reference clock the accuracy can reach one microsecond.

       chronyd can also operate as an RFC1305-compatible NTP server and peer.

       chronyc(1), chrony(1)

       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 @VERSION@		  @MAN_DATE@			     CHRONY(1)

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