A quick post on setting up a local NTP server with Debian 10
Install the ntp package:
$ sudo apt install ntp
Configure ntp to use for IPv4 only:
$ sudo nano /etc/default/ntp
NTPD_OPTS='-g -4'
Configure ntp servers and restrictions:
$ sudo nano /etc/ntp.conf
# You do need to talk to an NTP server or two (or three).
#server ntp.your-provider.example
server ntp.pagasa.dost.gov.ph
# pool.ntp.org maps to about 1000 low-stratum NTP servers. Your server will
# pick a different set every time it starts up. Please consider joining the
# pool: <http://www.pool.ntp.org/join.html>
#pool 0.debian.pool.ntp.org iburst
#pool 1.debian.pool.ntp.org iburst
#pool 2.debian.pool.ntp.org iburst
#pool 3.debian.pool.ntp.org iburst
# Example allow access from 192.168.1.0/24 and 172.16.1.0/24 clients
restrict 192.168.1.0 mask 255.255.255.0 nomodify notrap nopeer
restrict 172.16.1.0 mask 255.255.255.0 nomodify notrap nopeer
Allow access to 123/UDP on your firewall.
Sample: $ sudo iptables -A udp_inbound -p UDP -s 0/0 --dport 123 -j ACCEPT
Test ntp server:
$ ntpq -p
remote refid st t when poll reach delay offset jitter
==============================================================================
121.58.193.100 .GPS. 1 u 22 64 1 124.686 -145.97 0.000
Setting time to your client (requires ntpdate package):
$ sudo ntpdate 172.16.1.1
10 May 21:09:41 ntpdate[1519]: step time server 172.16.1.1 offset 0.814652 sec
Replace 172.16.1.1 to your NTP server IP Address.
References:
https://kifarunix.com/setup-ntp-server-using-ntpd-on-debian-10-buster/
https://www.tecmint.com/install-and-configure-ntp-server-client-in-debian/