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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timesyncd.conf

TIMESYNCD.CONF(5)						  timesyncd.conf						 TIMESYNCD.CONF(5)

NAME

       timesyncd.conf, timesyncd.conf.d - Network Time Synchronization configuration files

SYNOPSIS

       /etc/systemd/timesyncd.conf

       /etc/systemd/timesyncd.conf.d/*.conf

       /run/systemd/timesyncd.conf.d/*.conf

       /usr/lib/systemd/timesyncd.conf.d/*.conf

DESCRIPTION

       These configuration files control NTP network time synchronization.

CONFIGURATION DIRECTORIES AND PRECEDENCE

       The default configuration is defined during compilation, so a configuration file is only needed when it is necessary to deviate from those
       defaults. By default, the configuration file in /etc/systemd/ contains commented out entries showing the defaults as a guide to the
       administrator. This file can be edited to create local overrides.

       When packages need to customize the configuration, they can install configuration snippets in /usr/lib/systemd/*.conf.d/. Files in /etc/
       are reserved for the local administrator, who may use this logic to override the configuration files installed by vendor packages. The main
       configuration file is read before any of the configuration directories, and has the lowest precedence; entries in a file in any
       configuration directory override entries in the single configuration file. Files in the *.conf.d/ configuration subdirectories are sorted
       by their filename in lexicographic order, regardless of which of the subdirectories they reside in. When multiple files specify the same
       option, for options which accept just a single value, the entry in the file with the lexicographically latest name takes precedence. For
       options which accept a list of values, entries are collected as they occur in files sorted lexicographically. It is recommended to prefix
       all filenames in those subdirectories with a two-digit number and a dash, to simplify the ordering of the files.

       To disable a configuration file supplied by the vendor, the recommended way is to place a symlink to /dev/null in the configuration
       directory in /etc/, with the same filename as the vendor configuration file.

OPTIONS

       The following settings are configured in the "[Time]" section:

       NTP=
	   A space-separated list of NTP server host names or IP addresses. During runtime this list is combined with any per-interface NTP
	   servers acquired from systemd-networkd.service(8). systemd-timesyncd will contact all configured system or per-interface servers in
	   turn until one is found that responds. When the empty string is assigned, the list of NTP servers is reset, and all assignments prior
	   to this one will have no effect. This setting defaults to an empty list.

       FallbackNTP=
	   A space-separated list of NTP server host names or IP addresses to be used as the fallback NTP servers. Any per-interface NTP servers
	   obtained from systemd-networkd.service(8) take precedence over this setting, as do any servers set via NTP= above. This setting is
	   hence only used if no other NTP server information is known. When the empty string is assigned, the list of NTP servers is reset, and
	   all assignments prior to this one will have no effect. If this option is not given, a compiled-in list of NTP servers is used instead.

       RootDistanceMaxSec=
	   Maximum acceptable root distance. Takes a time value (in seconds). Defaults to 5 seconds.

       PollIntervalMinSec=, PollIntervalMaxSec=
	   The minimum and maximum poll intervals for NTP messages. Each setting takes a time value (in seconds).  PollIntervalMinSec= must not be
	   smaller than 16 seconds.  PollIntervalMaxSec= must be larger than PollIntervalMinSec=.  PollIntervalMinSec= defaults to 32 seconds, and
	   PollIntervalMaxSec= defaults to 2048 seconds.

SEE ALSO

       systemd(1), systemd-timesyncd.service(8), systemd-networkd.service(8)

systemd 237															 TIMESYNCD.CONF(5)

Red Hat