NTP howto - Revision history

Jca: /* If offset is too big */

2025-05-06T15:11:37Z

If offset is too big

← Older revision		Revision as of 17:11, 6 May 2025
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	NB! It is customary to use the default gateway as an NTP server on stationary networks, but at DTU, this is no longer done (for security reasons). Instead, use <code> ntp.ait.dtu.dk</code>.		NB! It is customary to use the default gateway as an NTP server on stationary networks, but at DTU, this is no longer done (for security reasons). Instead, use <code> ntp.ait.dtu.dk</code>.
	ntpdate -u ntp.ait.dtu.dk		ntpdate -u ntp.ait.dtu.dk
	ntpdate -u pool.ntp.org (if not on DTU net)		ntpdate -u pool.ntp.org (if not on DTU net, but on the internet)

	===If stratum is 16 or no '*' in first column===		===If stratum is 16 or no '*' in first column===

Jca: /* If offset is too big */

2025-05-06T15:10:44Z

If offset is too big

← Older revision		Revision as of 17:10, 6 May 2025
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	The accuracy is typically better than 1 ms.		The accuracy is typically better than 1 ms.

	NB! ~~on stationary networks it~~ is customary to use default gateway as NTP server, but at DTU this is no longer done (for security reasons). Instead use <code>ntp.ait.dtu.dk</code>.		NB! It is customary to use the default gateway as an NTP server on stationary networks, but at DTU, this is no longer done (for security reasons). Instead, use <code> ntp.ait.dtu.dk</code>.
	ntpdate -u ntp.ait.dtu.dk		ntpdate -u ntp.ait.dtu.dk
			ntpdate -u pool.ntp.org (if not on DTU net)

	===If stratum is 16 or no '*' in first column===		===If stratum is 16 or no '*' in first column===

Sh at 10:09, 5 August 2019

2019-08-05T10:09:18Z

← Older revision		Revision as of 12:09, 5 August 2019
Line 40:		Line 40:
	The accuracy is typically better than 1 ms.		The accuracy is typically better than 1 ms.

	NB! on stationary networks it is customary to use default gateway as NTP server, e.g.:		NB! on stationary networks it is customary to use default gateway as NTP server, but at DTU this is no longer done (for security reasons). Instead use <code>ntp.ait.dtu.dk</code>.
	~~ntpdate -u 10~~.59.8.~~1 (or)~~		ntpdate -u ntp.ait.dtu.dk
	ntpdate -u ~~192~~.38.66.1

	===If stratum is 16 or no '*' in first column===		===If stratum is 16 or no '*' in first column===

Jca: /* Configuration of slave computer */

2018-10-25T08:50:13Z

Configuration of slave computer

← Older revision		Revision as of 10:50, 25 October 2018
Line 87:		Line 87:
	# file /etc/ntp.conf		# file /etc/ntp.conf
	#		#
	# ~~server~~ ~~192~~.38.66.1		# pool ntp.ait.dtu.dk
	~~server 10.59.8.1~~		pool 192.168.0.210
	~~server~~ 192.168.0.210
	#		#
	#driftfile /etc/ntp/drift		#driftfile /etc/ntp/drift

Jca: /* Quick instructions */

2015-09-29T15:12:21Z

Quick instructions

← Older revision		Revision as of 17:12, 29 September 2015
Line 9:		Line 9:
	==Quick instructions==		==Quick instructions==

	Assuming two computers are to be synchronized, one called master (192.168.1.10) and the other slave (192.168.1.20).		Assuming two computers are to be synchronized, one called master (192.168.0.210 (smr default)) and the other slave (192.168.0.20).
			If on one of the campus networks, use the network gateway as time server, here 10.59.8.1 is a fine stratum 4 server, and all other NTP servers are blocked on this network.

	===Are master and slave running OK===		===Are master and slave running OK===

Jca: /* Configuration of slave computer */

2015-09-29T14:57:52Z

Configuration of slave computer

← Older revision		Revision as of 16:57, 29 September 2015
Line 94:		Line 94:
	#broadcastdelay 0.008		#broadcastdelay 0.008

			After the change restart the NTP

			sudo service ntp restart

	The ''driftfile'' is the place where ntpd saves the adjustment to the local clock to maintain it at the same speed as the reference computers clock. NB! there is only one drift value, so if the computer has to keep sync with different computers, where these computers may drift at a a different rate, then ntpd will use 'very' long time to readjust to the new source. That is once is gets used to the errors in the PC89 clock source, and then is reconfigured to a sutuation where 192.168.1.10 is available and PC89 is not, then this will probably drift with a quite different value - and require maybe 8-20 hours to get back into sync.		The ''driftfile'' is the place where ntpd saves the adjustment to the local clock to maintain it at the same speed as the reference computers clock. NB! there is only one drift value, so if the computer has to keep sync with different computers, where these computers may drift at a a different rate, then ntpd will use 'very' long time to readjust to the new source. That is once is gets used to the errors in the PC89 clock source, and then is reconfigured to a sutuation where 192.168.1.10 is available and PC89 is not, then this will probably drift with a quite different value - and require maybe 8-20 hours to get back into sync.

Jca: /* Start of slave */

2015-09-29T14:55:30Z

Start of slave

← Older revision		Revision as of 16:55, 29 September 2015
Line 98:		Line 98:

	The restrict part and other parts of the configuration file are commented out.		The restrict part and other parts of the configuration file are commented out.

	~~===Start of slave===~~

	~~The ntpd may be started automatically - on a slackware distribution the a starter script must be present in the /etc/rc.d directory, like this~~

	~~$ '''ls /etc/rc.d/rc.ntpd -l'''~~
	~~-rwxr-xr-x 1 root root 8331 2007-01-22 16:53 /etc/rc.d/rc.ntpd~~

	~~If it is executable, then it is started at boot time.~~

	==Configuration of master computer==		==Configuration of master computer==

Jca: /* Configuration of slave computer */

2015-09-29T14:54:47Z

Configuration of slave computer

← Older revision		Revision as of 16:54, 29 September 2015
Line 82:		Line 82:
	/etc/ntp.conf		/etc/ntp.conf

	On the computer that should be synchronized the configuration file ~~could look~~ like ~~(some comments removed)~~:		On the computer that should be synchronized the configuration file should add local time servers, like:

	# file /etc/ntp.conf		# file /etc/ntp.conf
	#		#
	# server 192.38.66.1		# server 192.38.66.1
	# server 10.59.8.1		server 10.59.8.1
	server 192.168.1.10		server 192.168.0.210
	~~server pc89~~
	~~#server kalman~~
	#		#
	driftfile /etc/ntp/drift		#driftfile /etc/ntp/drift
	multicastclient # listen on default 224.0.1.1		#multicastclient # listen on default 224.0.1.1
	broadcastdelay 0.008		#broadcastdelay 0.008

	~~The ''server'' part shows in this case two clock sources, the 192.168.1.10 and the PC89.~~

	~~The server pc89 is the one to use in this example, as the 192.168.1.10 is not available in this test setup. In the 'ntpq -p' above the 192.168.1.10 has never had a successful update.~~

	The ''driftfile'' is the place where ntpd saves the adjustment to the local clock to maintain it at the same speed as the reference computers clock. NB! there is only one drift value, so if the computer has to keep sync with different computers, where these computers may drift at a a different rate, then ntpd will use 'very' long time to readjust to the new source. That is once is gets used to the errors in the PC89 clock source, and then is reconfigured to a sutuation where 192.168.1.10 is available and PC89 is not, then this will probably drift with a quite different value - and require maybe 8-20 hours to get back into sync.		The ''driftfile'' is the place where ntpd saves the adjustment to the local clock to maintain it at the same speed as the reference computers clock. NB! there is only one drift value, so if the computer has to keep sync with different computers, where these computers may drift at a a different rate, then ntpd will use 'very' long time to readjust to the new source. That is once is gets used to the errors in the PC89 clock source, and then is reconfigured to a sutuation where 192.168.1.10 is available and PC89 is not, then this will probably drift with a quite different value - and require maybe 8-20 hours to get back into sync.

Jca at 14:47, 29 September 2015

2015-09-29T14:47:20Z

← Older revision		Revision as of 16:47, 29 September 2015
Line 1:		Line 1:
	This is a short description on how to make two computers have the same clock using NTP (Network Time Protocol)		This is a short description on how to make two computers have the same clock using NTP (Network Time Protocol)

			==Packages==

			Install NTP and NTPDATE

			sudo apt-get install ntp ntpdate

	==Quick instructions==		==Quick instructions==

Jca: /* If stratum is 16 or no '' in first column /

2012-07-11T10:07:25Z

If stratum is 16 or no '*' in first column

← Older revision		Revision as of 12:07, 11 July 2012
Line 42:		Line 42:
	Restart the ntpd daemon on the slave (as root):		Restart the ntpd daemon on the slave (as root):

	/etc/rc.d/ntpd restart		/etc/rc.d/ntpd restart (slackware)
			/etc/init.d/ntp restart (ubuntu)

	After another 4 minutes, the situation should be as shown above.		After another 4 minutes, the situation should be as shown above.

NTP howto - Revision history

Jca: /* If offset is too big */

Jca: /* If offset is too big */

Sh at 10:09, 5 August 2019

Jca: /* Configuration of slave computer */

Jca: /* Quick instructions */

Jca: /* Configuration of slave computer */

Jca: /* Start of slave */

Jca: /* Configuration of slave computer */

Jca at 14:47, 29 September 2015

Jca: /* If stratum is 16 or no '*' in first column */

Jca: /* If stratum is 16 or no '' in first column /