NAME

       chrony - programs for keeping computer clocks accurate

SYNOPSIS

       chronyc [OPTIONS]

       chronyd [OPTIONS]

DESCRIPTION

       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/intermittent  access  to  the Internet, and it can also act as an
       RFC1305-compatible NTP server.

USAGE

       chronyc is a command-line interface  program  which  can  be  used  to  monitor  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 accordingly.  It also works out the rate  at
       which  the  system clock gains or loses time and uses this information to keep it accurate
       between measurements 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 Protocol is http://www.ntp.org.

       It is designed so that it can work on computers which only  have  intermittent  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 performance, 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 session 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.

SEE ALSO

       chronyc(1), chrony(1)

       http://chrony.tuxfamily.org/

AUTHOR

       Richard Curnow <rc@rc0.org.uk>

       This  man-page  was  written  by  Jan  Schaumann <jschauma@netmeister.org> as part of "The
       Missing Man Pages Project".  Please see http://www.netmeister.org/misc/m2p2/index.html for
       details.

       The complete chrony documentation is supplied in texinfo format.