NTP Server Configuration: ntp.conf File

This file, /etc/ntp.conf, provides configuration settings for the ntpd daemon, which is responsible for synchronizing your system's time with accurate time sources. This guide outlines the key configuration options and their usage.

Drift File:

driftfile /var/lib/ntp/ntp.drift

This line specifies the location of the ntp.drift file, which stores records of the system clock's drift. This information is helpful for analyzing and adjusting timekeeping accuracy.

Leap Second Definitions:

leapfile /usr/share/zoneinfo/leap-seconds.list

The leapfile directive points to a file containing the latest information on leap seconds, ensuring that your system accurately accounts for these adjustments in time.

Statistics Logging:

# Enable this if you want statistics to be logged.
#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

By uncommenting the statsdir line and specifying a directory, you can enable logging of various statistics, including loop statistics, peer statistics, and clock statistics. The filegen directives specify the format and frequency of the log files.

Time Server Selection:

# Specify one or more NTP servers.

# Use servers from the NTP Pool Project. Approved by Ubuntu Technical Board
# on 2011-02-08 (LP: #104525). See http://www.pool.ntp.org/join.html for
# more information.
#pool 0.ubuntu.pool.ntp.org iburst
#pool 1.ubuntu.pool.ntp.org iburst
#pool 2.ubuntu.pool.ntp.org iburst
#pool 3.ubuntu.pool.ntp.org iburst


server 0.asia.pool.ntp.org iburst
server 1.asia.pool.ntp.org iburst
server 2.asia.pool.ntp.org iburst
server 3.asia.pool.ntp.org iburst


# Use Ubuntu's ntp server as a fallback.
pool ntp.ubuntu.com

The server and pool directives define the time sources that your system will use for synchronization. The example above uses servers from the NTP Pool Project, offering a robust and geographically diverse set of time servers. The iburst option requests a burst of synchronization packets for quicker time acquisition.

Access Control:

# Access control configuration; see /usr/share/doc/ntp-doc/html/accopt.html for
# details.  The web page <http://support.ntp.org/bin/view/Support/AccessRestrictions>
# might also be helpful.
#
# Note that 'restrict' applies to both servers and clients, so a configuration
# that might be intended to block requests from certain clients could also end
# up blocking replies from your own upstream servers.

# By default, exchange time with everybody, but don't allow configuration.
restrict -4 default kod notrap nomodify nopeer noquery limited
restrict -6 default kod notrap nomodify nopeer noquery limited

# Local users may interrogate the ntp server more closely.
restrict 127.0.0.1
restrict ::1

# Needed for adding pool entries
restrict source notrap nomodify noquery

# Clients from this (example!) subnet have unlimited access, but only if
# cryptographically authenticated.
#restrict 192.168.123.0 mask 255.255.255.0 notrust


# If you want to provide time to your local subnet, change the next line.
# (Again, the address is an example only.)
#broadcast 192.168.123.255

# 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
#broadcastclient

The restrict directives define access control rules for the NTP server. The default rule limits access for all clients, allowing only time exchanges without allowing configuration changes. The 127.0.0.1 and ::1 rules grant local users more access, while the source rule allows adding new pool entries. The notrust option in the commented example requires cryptographic authentication for clients from the specified subnet.

Time Broadcasts:

#Changes recquired to use pps synchonisation as explained in documentation:
#http://www.ntp.org/ntpfaq/NTP-s-config-adv.htm#AEN3918

#server 127.127.8.1 mode 135 prefer    # Meinberg GPS167 with PPS
#fudge 127.127.8.1 time1 0.0042        # relative to PPS for my hardware

#server 127.127.22.1                   # ATOM(PPS)
#fudge 127.127.22.1 flag3 1            # enable PPS API

The broadcast directive enables the server to provide time to the specified subnet. The commented lines related to disable auth and broadcastclient allow the server to receive time broadcasts from other machines on the network, but this should only be done if you trust all machines on the network.

Hardware Clock Synchronization:

The commented examples illustrate how to synchronize with hardware clocks like a Meinberg GPS167 or ATOM(PPS) using the server and fudge directives. The fudge directive allows you to adjust the server's time based on the hardware clock's specific characteristics.

By configuring the ntp.conf file correctly, you ensure that your system has accurate timekeeping, essential for many critical system functions. For detailed information about specific configuration options, refer to the documentation linked throughout this guide.