Name

ntp.conf − Network Time Protocol configuration file

Description

The /etc/ntp.conf file is the configuration file for the Network Time Protocol (NTP) daemon, ntpd. This file must be configured on your system before running ntpd.

Note

Any host names that you specify in the /etc/ntp.conf file must have an entry in the /etc/hosts file, or an entry in the master hosts database, if the database is being served to your system by BIND/Hesiod or Yellow Pages.

The /etc/ntp.conf 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.  Digital recommends that all systems include the trusting no 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 synchronization.   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 peer 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 synchronization.  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 server 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 systems.  At most, one system in a set of nodes running ntpd should be identified as a local reference clock.

A host which specifies this entry should not specify any peer or server entries.

Examples

This is a sample configuration file for an NTP client which receives time synchronization from the NTP servers: server1, server2, and server3. 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.
#
#peerserver1
#peerserver2
#peerserver3
#
#
#
#
#    **  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.
#
serverserver1
serverserver2
serverserver3
#
#
#
#    **  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/nullLOCL1-5local
#

See Also

ntp(1), ntpd(8), ntpdc(8)
RFC 1129—Internet time synchronization:  The Network Time Protocol
Introduction to Networking and Distributed System Services