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

6       chrony - programs for keeping computer clocks accurate
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SYNOPSIS

10       chronyc [OPTIONS]
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12       chronyd [OPTIONS]
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DESCRIPTION

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

29       chronyc is a command-line interface program which can be used to  moni‐
30       tor  chronyd's  performance  and to change various operating parateters
31       whilst it is running.
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33       chronyd's main function is to obtain measurements  of  the  true  (UTC)
34       time  from one of several sources, and correct the system clock accord‐
35       ingly.  It also works out the rate at which the system clock  gains  or
36       loses  time  and uses this information to keep it accurate between mea‐
37       surements from the reference.
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39       The reference time can be derived from  either  Network  Time  Protocol
40       (NTP)   servers,  reference  clocks,  or  wristwatch-and-keyboard  (via
41       chronyc).  The main source of information about the Network Time Proto‐
42       col is http://www.eecis.udel.edu/~ntp.
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44       It  is designed so that it can work on computers which only have inter‐
45       mittent access to reference sources, for example computers which use  a
46       dial-up  account  to  access  the Internet.  Of course, it will work on
47       computers with permanent connections too.
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49       In addition, for Linux 2.0.x (for x >= 32) or 2.2 onwards, chronyd  can
50       monitor  the  system's  real  time clock performance, so the system can
51       maintain accurate time even across reboots.
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53       Typical accuracies available between 2 machines are
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55       On an ethernet LAN : 100-200  microseconds,  often  much  better  On  a
56       V32bis  dial-up  modem connection : 10's of milliseconds (from one ses‐
57       sion to the next)
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59       With a good reference clock the accuracy can reach one microsecond.
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61       chronyd can also operate as an RFC1305-compatible NTP server and peer.
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SEE ALSO

65       chronyc(1), chrony(1)
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67       http://chrony.tuxfamily.org/
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AUTHOR

71       Richard Curnow <rc@rc0.org.uk>
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73       This man-page was written by Jan Schaumann <jschauma@netmeister.org> as
74       part  of  "The  Missing Man Pages Project".  Please see http://www.net‐
75       meister.org/misc/m2p2/index.html for details.
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77       The complete chrony documentation is supplied in texinfo format.
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82chrony                         December 04, 2009                     CHRONY(1)
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