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Configuring NTP On Your Linux Server by amatamazon


									The Network Time Protocol (NTP) defines a set of algorithms for the
dissemination of time across the Internet. The NTP protocol can be used
to synchronise the system time on your Linux Server with a highly
accurate Internet time reference.This article describes how to configure
the Network Time Protocol (NTP) daemon on your Linux server to
synchronise with an Internet based NTP server. It also provides a list of
well-know public Internet time references.Obtaining the NTP Source Code
DistributionThe Linux NTP source code distribution is publicly available
'open source' software. The distribution can be freely downloaded from
the NTP web site ''. The latest NTP version for Linux is 2.4.2. A
port is also available for Windows platforms, but the primary development
platform for NTP is the Linux operating system. A number of Linux based
operating systems such as Mandrake and Redhat offer NTP as an installable
RPM package.Once download is complete, the NTP distribution should be
configured and compiled on the host computer.

Configuration of the NTP DaemonThe NTP daemon is configured through
entries in the primary NTP configuration file 'ntp.conf'. The NTP
configuration file contains a list of commands that instruct the daemon
to synchronise with a specified NTP server. NTP servers are specified
using the 'server' command followed by the domain name of the server
thus:server number of access
control options are also available to restrict the use of your NTP server
by network time clients.

To only allow machines on your own network to synchronize with the server
use:restrict mask nomodify notrapAlternatively,
you can restrict all access to your NTP server with the following
command:restrict default ignoreMultiple directives can be specified to
restrict access to a specified range of computers.Using NTP
AuthenticationNTP authentication is used by time clients to authenticate
the time server to prevent rogue server intervention. NTP authentication
is based on encrypted keys. A key is encrypted and sent to the client by
the server, where it is unencrypted and checked against the client key to
ensure a match.NTP keys are stored in the 'ntp.keys' file in the
following format:Key-number M Key      (The M stands for MD5 encryption),
e.g.:1 M secret5 M RaBBit7 M TiMeLy10 M MYKEYThe NTP configuration
file 'ntp.conf' specifies which of the keys are trusted. Any keys
specified in the keys file but not trusted will not be used for
authentication, e.g.:trustedkey 1 7 10NTP Client Authentication
ConfigurationThe NTP client also needs to be configured with similar
authentication information as the server. The client may use a subset of
the keys specified on the server. A different subset of keys can also be
used on different clients, e.g.:Client A)         Client B)1 M secret
1 M secret7 M TiMeLy        5 M RaBBittrustedkey 1 7    trustedkey
1Controlling the NTP Server DaemonOnce configured, the NTP daemon can be
controlled using the commands: 'ntpd start'; 'ntpd stop' and 'ntpd
restart'.Querying the NTP Server DaemonThe NTP server daemon can be
queried using the 'ntpq -p' command. The ntpq command queries the NTP
server for synchronisation status and provides a list of servers with
synchronisation information for each server.Public Internet NTP
ServersPublic NTP servers provide subscription free, highly accurate,
timing references for computer time synchronisation. Below is a list of
popular public NTP time servers.Stratum 1 Public NTP - - Computing Systems Research Ltd.
United Kingdom - NTP V4 primary (Odetics GPS), Sun/Sparc Solaris - - Falmouth, Cornwall, UK - NTP
V4.2.0 primary (MSF Radio Clock Receiver), Trustix LinuxStratum 2 Public
NTP - - Telehouse Europe, London
E14 - NTP V4 secondary Sun UltraSPARC Solaris - - University of Manchester, Manchester, England - NTP
secondary (S2), SGI/ - - University of
Manchester, Manchester, England - NTP secondary (S2),
PC/ - - ExNet Ltd, London, UK - NTP
secondary (stratum 2), Sun-4/Unix - - Interhouse London E14 - NTP V4,
SuSE 9.0 (Stratum 1) - - Telehouse Europe, London E14 - NTP V4
secondary Sun UltraSPARC Solaris - University of
Strathclyde, Glasgow, Scotland - NTP V4 - - Telehouse Europe, London E14 - NTP V4 secondary Sun
UltraSPARC Solaris 8

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