Network Clock Synchronization

We use chrony to synchronize the clocks of computers over a network.

$ apt-get install chrony

If you're running on an disconnected network you will have to manually download then install the chrony package.  

$ aptitude download chrony timelimit

will download the two required packages to the current directory. Make sure to perform this command on a machine with the same architecture that you plan to install chrony on (I.E. i386, amd64 or armel).

To set up a topside, first install then edit the configuration file. A sample configuration file for a master clock — I.E. the machine that will always be on before the clients

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keyfile /etc/chrony/chrony.keys
commandkey 1
driftfile /var/lib/chrony/chrony.drift
local stratum 8
allow 10/8       # allow anyone with a 10.x.x.x address to sync to us
allow 192.168/16 # allow anyone with a 192.168.x.x address to sync to us
allow 172.16/12  # allow any loopback address to sync to us
manual

To test the server:

$ ntpdate timeserver_ip

To setup a client first make sure you have IP access to the master and that the master is working.

Linux clients should edit /etc/hosts to include a line like

timeserver IP.OF.MASTER.CLOCK

Set up the chrony.conf file in /etc/chrony/chrony.conf

A sample configuration file for a topside slave clock

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server timeserver
initstepslew 20 timeserver
driftfile /var/lib/chrony/chrony.drift
keyfile /etc/chrony/chrony.keys
commandkey 1
local stratum 12
allow 10/8
allow 192.168/16
allow 172.16/12

A sample configuration file for a TS4710 slave clock:

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server timeserver
initstepslew 20 timeserver
linux_hz 100 # this is absolutely REQUIRED!
driftfile /persistent/chrony.drift
keyfile /etc/chrony/chrony.keys
commandkey 1
local stratum 12
allow 10/8
allow 192.168/16
allow 172.16/12

To have chrony startup on boot on a debian topside do

# update-rc.d chrony start 20 2 3 4 5 . stop 20 0 1 6 .

or add

/etc/init.d/chrony start

to /etc/rc.local

Testing

First, is it running?

$ ps aux | grep chronyd

On unsynchronized machines you should be able to

$ntpdate machine_ip

To see if a client is synchronized to the server 

$chronyc tracking

and you should see the master's IP in 'Reference ID'.  It may take a few minutes.

Initial Synchronization

When the clock is in an unknown state it is often preferred to manually synchronize the clock before starting chrony.

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sudo /etc/init.d/chrony stop
sudo ntpdate timeserver
sudo /etc/init.d/chrony start