In this tutorial, we will be discussing how to install and configure **Chrony** , an alternative NTP client and server for Unix-like systems. Chrony can synchronise the system clock faster with better time accuracy and it can be particularly useful for the systems which are not online all the time. Chrony is free, open source and supports GNU/Linux and BSD variants such as FreeBSD, NetBSD, macOS, and Solaris.
### Installing Chrony
Chrony is available in the default repositories of most Linux distributions. If you’re on Arch Linux, run the following command to install it:
```
$ sudo pacman -S chrony
```
On Debian, Ubuntu, Linux Mint:
```
$ sudo apt-get install chrony
```
On Fedora:
```
$ sudo dnf install chrony
```
Once installed, start **chronyd.service** daemon if it is not started already:
```
$ sudo systemctl start chronyd.service
```
Make it to start automatically on every reboot using command:
```
$ sudo systemctl enable chronyd.service
```
To verify if the Chronyd.service has been started, run:
```
$ sudo systemctl status chronyd.service
```
If everything is OK, you will see an output something like below.
```
● chrony.service - chrony, an NTP client/server
Loaded: loaded (/lib/systemd/system/chrony.service; enabled; vendor preset: ena
Active: active (running) since Wed 2018-10-17 10:34:53 UTC; 3min 15s ago
Docs: man:chronyd(8)
man:chronyc(1)
man:chrony.conf(5)
Main PID: 2482 (chronyd)
Tasks: 1 (limit: 2320)
CGroup: /system.slice/chrony.service
└─2482 /usr/sbin/chronyd
Oct 17 10:34:53 ubuntuserver systemd[1]: Starting chrony, an NTP client/server...
Oct 17 10:34:53 ubuntuserver chronyd[2482]: chronyd version 3.2 starting (+CMDMON
Oct 17 10:34:53 ubuntuserver chronyd[2482]: Initial frequency -268.088 ppm
Oct 17 10:34:53 ubuntuserver systemd[1]: Started chrony, an NTP client/server.
Oct 17 10:35:03 ubuntuserver chronyd[2482]: Selected source 85.25.84.166
Oct 17 10:35:03 ubuntuserver chronyd[2482]: Source 85.25.84.166 replaced with 2403
Oct 17 10:35:03 ubuntuserver chronyd[2482]: Selected source 91.189.89.199
Oct 17 10:35:06 ubuntuserver chronyd[2482]: Selected source 106.10.186.200
```
As you can see, Chrony service is started and working!
### Configure Chrony
The NTP clients needs to know which NTP servers it should contact to get the current time. We can specify the NTP servers in the **server** or **pool** directive in the NTP configuration file. Usually, the default configuration file is **/etc/chrony/chrony.conf** or **/etc/chrony.conf** depending upon the Linux distribution version. For better reliability, it is recommended to specify at least three servers.
The following lines are just an example taken from my Ubuntu 18.04 LTS server.
```
[...]
# About using servers from the NTP Pool Project in general see (LP: #104525).
# Approved by Ubuntu Technical Board on 2011-02-08.
# See http://www.pool.ntp.org/join.html for more information.
pool ntp.ubuntu.com iburst maxsources 4
pool 0.ubuntu.pool.ntp.org iburst maxsources 1
pool 1.ubuntu.pool.ntp.org iburst maxsources 1
pool 2.ubuntu.pool.ntp.org iburst maxsources 2
[...]
```
As you see in the above output, [**NTP Pool Project**][1] has been set as the default time server. For those wondering, NTP pool project is the cluster of time servers that provides NTP service for tens of millions clients across the world. It is the default time server for Ubuntu and most of the other major Linux distributions.
Here,
* the **iburst** option is used to speed up the initial synchronisation.
* the **maxsources** refers the maximum number of NTP sources.
Please make sure that the NTP servers you have chosen are well synchronised, stable and close to your location to improve the accuracy of the time with NTP sources.
### Manage Chronyd from command line
Chrony has a command line utility named **chronyc** to control and monitor the **chrony** daemon (chronyd).
To check if **chrony** is synchronized, we can use the **tracking** command as shown below.
```
$ chronyc tracking
Reference ID : 6A0ABAC8 (t1.time.sg3.yahoo.com)
Stratum : 3
Ref time (UTC) : Wed Oct 17 11:48:51 2018
System time : 0.000984587 seconds slow of NTP time
Last offset : -0.000912981 seconds
RMS offset : 0.007983995 seconds
Frequency : 23.704 ppm slow
Residual freq : +0.006 ppm
Skew : 1.734 ppm
Root delay : 0.089718960 seconds
Root dispersion : 0.008760406 seconds
Update interval : 515.1 seconds
Leap status : Normal
```
We can verify the current time sources that chrony uses with command:
```
$ chronyc sources
210 Number of sources = 8
MS Name/IP address Stratum Poll Reach LastRx Last sample
If your system is not connected to Internet, you need to notify Chrony that the system is not connected to the Internet. To do so, run:
```
$ sudo chronyc offline
[sudo] password for sk:
200 OK
```
To verify the status of your NTP sources, simply run:
```
$ chronyc activity
200 OK
0 sources online
8 sources offline
0 sources doing burst (return to online)
0 sources doing burst (return to offline)
0 sources with unknown address
```
As you see, all my NTP sources are down at the moment.
Once you’re connected to the Internet, just notify Chrony that your system is back online using command:
```
$ sudo chronyc online
200 OK
```
To view the status of NTP source(s), run:
```
$ chronyc activity
200 OK
8 sources online
0 sources offline
0 sources doing burst (return to online)
0 sources doing burst (return to offline)
0 sources with unknown address
```
For more detailed explanation of all options and parameters, refer the man pages.
```
$ man chronyc
$ man chronyd
```
And, that’s all for now. Hope this was useful. In the subsequent tutorials, we will see how to setup a local NTP server using Chrony and configure the clients to use it to synchronise time.
