NTP Server issue

Operating Systems Linux Red Hat NTP Server issue

09-24-2013

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It is possible to have a NTP server running on VMware (5.1 in my case). But you have to make sure, that the host's clock is close to accurate, meaning ESXi's NTP client has to be configured properly.

That's because a VM syncs its time with the host at boot time, even if timesync is disabled in the VMs configuration. Now if the host's time is off by a greater timespan, the guest's clock is off too, because of the boot-time timesync with the host and the NTP daemon will not be able to adjust the guest's clock and synchronize to it's upstream NTP servers.

Last edited by hergp; 09-24-2013 at 06:55 AM.. Reason: some rephrasing

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ntp.conf

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)

Red Hat