Network Time Protocol

This entry was posted by Friday, 22 May, 2009
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The Network Time Protocol (NTP) is a protocol for synchronizing the clocks of computer systems over packet-switched, variable-latency data networks. NTP uses UDP port 123 as its transport layer. It is designed particularly to resist the effects of variable latency (Jitter).

NTP is one of the oldest Internet protocols still in use (since before 1985). NTP was originally designed by Dave Mills of the University of Delaware, who still maintains it, along with a team of volunteers.

NTP: The Network Time Protocol
Network Time Protocol – Wikipeadia


I configure NTP via > Applications > System > Time and Date. Enable/Install NTP server from there.

New Zealand — To use this pool zone, add the following:


Skip to Sync Time and Start ntpd

Debian Install

apt-get install ntp ntp-simple ntp-server ntp-doc ntpdate
/etc/init.d/ntp stop

Debian Configure ntp.conf


# /etc/ntp.conf, configuration for ntpd

# ntpd will use syslog() if logfile is not defined
#logfile /var/log/ntpd

driftfile /var/lib/ntp/ntp.drift
statsdir /var/log/ntpstats/

statistics loopstats peerstats clockstats
filegen loopstats file loopstats type day enable
filegen peerstats file peerstats type day enable
filegen clockstats file clockstats type day enable

# You do need to talk to an NTP server or two (or three).

# ... and use the local system clock as a reference if all else fails
# NOTE: in a local network, set the local stratum of *one* stable server
# to 10; otherwise your clocks will drift apart if you lose connectivity.
fudge stratum 13

# By default, exchange time with everybody, but don't allow configuration.
# See /usr/share/doc/ntp-doc/html/accopt.html for details.
restrict default kod notrap nomodify nopeer noquery

# Local users may interrogate the ntp server more closely.
restrict nomodify

# Clients from this (example!) subnet have unlimited access,
# but only if cryptographically authenticated
#restrict  mask notrust

# If you want to provide time to your local subnet, change the next line.
# (Again, the address is an example only.)

# If you want to listen to time broadcasts on your local subnet,
# de-comment the next lines. Please do this only if you trust everybody
# on the network!
#disable auth

Sync Time and Start ntpd

Sync the system time to MLS’s ntp server.
Sync the system time to the CMOS hardware clock.
Start ntpd.

/etc/init.d/ntp stop
hwclock --systohc
/etc/init.d/ntp start

After several minutes, run the command ntpq -c pe to check that ntpd program is running correctly. The response should be something like this:

     remote           refid      st t when poll reach   delay   offset  jitter
+mx1.airstream.n    2 u   17   64  377   60.427    6.119  16.022
*ds001.hostingsh     2 u   15   64  377   81.001    3.360   2.382   2 u    1   64  377   56.908   54.138  32.835

The “reach” column should be greater than 0 and should increase with time (patience is good with ntp) to eventually reach 377 which is as high as it goes. The offset and jitter should not be 0.0000. In case of problems, consult the system log file to see if the program has written an error message.

A Word of Warning

What timezone is correct for your system? It depends on the geographical location of the machine. Getting the correct location is important, but the system must also know how your hardware clock is set. Most DOS based PCs set their hardware clock on Local Time, while most UNIX systems set their hardware clock to UTC.

The Debian GNU/Linux system gains its knowledge of this setting from the file /etc/default/rcS. This file contains either the line UTC=yes, which indicates that the hardware clock is set to UTC, or it contains the line UTC=no, which declares the hardware clock is set to Local Time. If these setting are correct, and the hardware clock is truly set as indicated, then configuring the proper timezone for the machine will cause the proper date and time to be displayed. If these are not set correctly, the the reported time will be quite incorrect. See hwclock(8) for more details on this topic.

Xubuntu is UTC=no, best for a dual boot with Windows setup.


The work done by tzconfig is actually pretty simple. It just copies the correct timezone installed in /usr/share/zoneinfo/ to /etc/localtime and puts the name of the timezone into /etc/timezone.

There is nothing wrong with doing this manually. However, using tzconfig you don’t have to remember the path to the timezones.

Link to my wiki on Network Time Protocol configuration []

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