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Operating Systems Linux Red Hat Auto NTP Time Synchronization Post 302581640 by mark54g on Tuesday 13th of December 2011 04:30:04 PM
Old 12-13-2011
Absolutely not using cron. ntpd is a daemon. It is constantly running and should be set up via an appropriate ntp.conf file to ensure that it stays within milliseconds, not minutes. You may need a step tickers and drift file, as well as statistics, but you can, with a good time source, be within about 20 milliseconds over the internet without much issue.

Personally, I would suggest you get a master clock, but if you don't need sync to be that tight, you can sync to the internet as long as there are not a lot of machines.

Quick HOWTO : Ch24 : The NTP Server - Linux Home Networking

You should not have to download it, but configure it as instructed.

Essentially, you will end up, with the appropriate configuration and init scripts, set up your server to slew the clock toward the appropriate time so that you are within a margin of error. The speed/latency to the internet does not actually matter as much as the differential between answers, and you should be polling those upstream lower stratum servers every few minutes to make sure you are not out of the ballpark. Then, the algorithm for ntp will be able to "Train" your clock on the server to stay within acceptable ranges by use of a drift file.
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SYSTEMD-TIMESYNCD.SERVICE(8)				     systemd-timesyncd.service				      SYSTEMD-TIMESYNCD.SERVICE(8)

NAME
systemd-timesyncd.service, systemd-timesyncd - Network Time Synchronization SYNOPSIS
systemd-timesyncd.service /lib/systemd/systemd-timesyncd DESCRIPTION
systemd-timesyncd is a system service that may be used to synchronize the local system clock with a remote Network Time Protocol server. It also saves the local time to disk every time the clock has been synchronized and uses this to possibly advance the system realtime clock on subsequent reboots to ensure it monotonically advances even if the system lacks a battery-buffered RTC chip. The systemd-timesyncd service specifically implements only SNTP. This minimalistic service will set the system clock for large offsets or slowly adjust it for smaller deltas. More complex use cases are not covered by systemd-timesyncd. The NTP servers contacted are determined from the global settings in timesyncd.conf(5), the per-link static settings in .network files, and the per-link dynamic settings received over DHCP. See systemd.network(5) for more details. timedatectl(1)'s set-ntp command may be used to enable and start, or disable and stop this service. FILES
/var/lib/systemd/timesync/clock This file contains the timestamp of the last successful synchronization. SEE ALSO
systemd(1), timesyncd.conf(5), systemd.network(5), systemd-networkd.service(8), timedatectl(1), localtime(5), hwclock(8) systemd 237 SYSTEMD-TIMESYNCD.SERVICE(8)
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