chrony

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net-misc/chrony is a versatile implementation of the Network Time Protocol (NTP). It can synchronize the system clock with NTP servers, reference clocks (e.g. GPS receiver), and manual input using wristwatch and keyboard. It can also operate as an NTPv4 (RFC 5905) server and peer to provide a time service to other computers in the network.

Installation

USE flags

USE flags for net-misc/chrony NTP client and server programs

adns Support for asynchronous DNS
cmdmon Support for command and monitoring
libedit Use the libedit library (replacement for readline)
ntp Support for the Network Time Protocol (NTP)
phc Support for the PTP (Precision Time Protocol) Hardware Clock (PHC) interface
pps Support for the Linux Pulse Per Second (PPS) interface
readline Enable support for libreadline, a GNU line-editing library that almost everyone wants
refclock Support for reference clocks
rtc Support for the Linux Real Time Clock interface

Emerge

Install the chrony package:

root #emerge --ask net-misc/chrony

Configuration

/etc/chrony/chrony.conf is the configuration file for chronyd. The default configuration is populated with:

FILE /etc/chrony/chrony.conf
# Use public NTP servers from the pool.ntp.org project.
pool pool.ntp.org iburst

# Record the rate at which the system clock gains/losses time.
driftfile /var/lib/chrony/drift

# In first three updates step the system clock instead of slew
# if the adjustment is larger than 1 second.
makestep 1.0 3

# Enable kernel synchronization of the real-time clock (RTC).
rtcsync

hwclockfile /etc/adjtime
Note
Time zones and location of the server do not matter for the NTP protocol; it synchronizes via UTC.

On systems where a network connection is not always available at boot (laptops, etc.), it might help to change the pool line in the server configuration:

FILE /etc/chrony/chrony.conf
pool pool.ntp.org iburst auto_offline

This tells chronyd that the machine will be assumed to have gone offline when 2 requests have been sent to it without receiving a response. You will need to use the chronyc online command to re-enable polling (See below)

Acting as a local NTP server

By default, chronyd only synchronizes the local machine time. By adding allow and deny rules, it will act as a local NTP source:

FILE /etc/chrony/chrony.conf
# Note order does not matter for this example, order does matter with 'allow all' or 'deny all'
# Allow a specific IP
allow 1.2.3.4
# Deny a certain subnet
deny 1.2.3
# Allow all of the 1.2.x.x subnet
allow 1.2

Usage

chronyc Client Interface Tool

chronyc is a command-line interface program which can be used to monitor chronyd's performance and to change various operating parameters whilst it is running. A full list of commands can be found in the manual, man 1 chronyc

Examples:

root #chronyc offline # Set all sources offline
root #chronyc online # Set all sources online

chronyd service

Add chronyd to the default runlevel to have the time synchronized automatically.

root #rc-service chronyd start
root #rc-update add chronyd default

To monitor status of the server:

root #rc-service chronyd status

See also

External resources