chrony(1) [centos man page]
CHRONY(1) User's Manual CHRONY(1) 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 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 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. chrony @VERSION@ @MAN_DATE@ CHRONY(1)
Check Out this Related Man Page
ntp.conf(5) File Formats Manual ntp.conf(5) Name ntp.conf - Network Time Protocol configuration file Description The file is the configuration file for the Network Time Protocol (NTP) daemon, This file must be configured on your system before running Any host names that you specify in the file must have an entry in the file, or an entry in the master database, if the database is being served to your system by BIND/Hesiod or Yellow Pages. The file has four entry formats: trusting no This entry guarantees that your system synchronizes only to the NTP servers identified in the peer and server entries specified. Dig- ital recommends that all systems include the entry. peer server This entry identifies server as one of the NTP servers that your system trusts, and from which your system will accept time synchro- nization. Your system may also provide time synchronization to this server. Servers can be identified by host name or internet address. NTP servers should be configured with entries. server server This entry identifies server as one of the NTP servers that your system trusts, and from which your system will accept time synchro- nization. Your system can not provide time synchronization to this server. Servers can be identified by host name or internet address. NTP clients should be configured with entries. peer /dev/null LOCL 1 -5 local This entry identifies your system as a local reference clock. A local reference clock is the most accurate system clock available at your site. If you receive time synchronization from the Internet NTP service, you should not include this entry on any of your sys- tems. At most, one system in a set of nodes running should be identified as a local reference clock. A host which specifies this entry should not specify any or entries. Examples This is a sample configuration file for an NTP client which receives time synchronization from the NTP servers: and Lines beginning with a number sign (#) are comments. # # NTP Configuration File # This file is mandatory for the ntpd daemon # # # # ** A L L ** # # "trusting no" prevents this host from synchronizing # to any host that is not listed below. It is recommended # that all hosts include the line "trusting no". # trusting no # # # ** S E R V E R ** # # If you are configuring a server, use "peer" entries to # synchronize to other NTP servers. For example, server1, # server2, and server3. # #peer server1 #peer server2 #peer server3 # # # # # ** C L I E N T ** # # If you are configuring a client, use "server" entries to # synchronize to NTP servers. For example, server1, server2, # and server3. # server server1 server server2 server server3 # # # # ** L O C A L R E F E R E N C E C L O C K ** # # If you are configuring a local reference clock, include the # following entry and the "trusting no" entry ONLY. # #peer /dev/null LOCL 1 -5 local # See Also ntp(1), ntpd(8), ntpdc(8) RFC 1129--Internet time synchronization: The Network Time Protocol Introduction to Networking and Distributed System Services ntp.conf(5)