Chrony - Synchronize the date and time of all host computers in a network without internet connection

Question

I have two machines,

1. host A with IP 192.168.0.1
2. host B with IP 192.168.0.2

They connected to the same network and I would like to set the date and time of machine B to match those of machine A. While I can set up the machines with an internet connection initially, they will not have access to it once deployed and they will be rebooted every day.

Current Approach using Chrony Reference.

This configuration is not correct, based on some test results, the synchronization succeeds when the NTP server has an internet connection and fails otherwise.

Do you have any advice or suggestions for configuring them effectively?

Machine A - Configured as NTP server

sudo apt update && sudo apt upgrade
sudo apt install chrony
sudo vim /etc/chrony/chrony.conf

Used this configuration to set up the NTP server

confdir /etc/chrony/conf.d
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
allow 192.168.0.0/24
sourcedir /run/chrony-dhcp
sourcedir /etc/chrony/sources.d
keyfile /etc/chrony/chrony.keys
driftfile /var/lib/chrony/chrony.drift
ntsdumpdir /var/lib/chrony
logdir /var/log/chrony
maxupdateskew 100.0
rtcsync
makestep 1 3
leapsectz right/UTC

Restarted the chrony service, checked that was running and enabled it to start on boot

sudo systemctl restart chrony
sudo systemctl status chrony
CTRL+C
sudo systemctl enable chrony

Machine B - Configured as Chrony Client

Synced the date and time with a pool of servers and set the 192.168.0.1

sudo apt update && sudo apt upgrade
sudo apt install chrony
sudo vim /etc/chrony/chrony.conf

Used the following configuration file

pool 192.168.0.1 iburst prefer
keyfile /etc/chrony/chrony.keys
driftfile /var/lib/chrony/chrony.drift
logdir /var/log/chrony
log measurements statistics tracking
maxupdateskew 100.0
rtcsync
makestep 1.0 3

Restarted, checked the service and enabled it at startup

sudo systemctl restart chrony
sudo systemctl status chrony
CTRL+C
sudo systemctl enable chrony

Update If I manually synchronize the time, I get the following error No suitable source for synchronisation.

sudo systemctl stop chrony 
sudo chronyd -d 'server 192.168.0.1 iburst'
2023-03-15T15:54:55Z chronyd version 3.5 starting (+CMDMON +NTP +REFCLOCK +RTC +PRIVDROP +SCFILTER +SIGND +ASYNCDNS +SECHASH +IPV6 -DEBUG)
2023-03-15T15:54:55Z Initial frequency -36.773 ppm
2023-03-15T15:55:03Z No suitable source for synchronisation
2023-03-15T15:55:03Z chronyd exiting

Update 2

If I connect the NTP server to internet, then the synchronization succeeds.

Answer 1

You need the directive local in the server config file for it to synchronize on its own when there is no internet. Typically, you might use local stratum 8 to say it is less good than a remote ntp server that might be stratum 2 or 3. This stops the local clock being preferred over the internet clock source. If the server has a hardware time source like a gps then look at the refclock directive to see if it can be configured in too.