NTP (Network Time Protocol)
Uses UDP connections and port 123.
Example installation in Ubuntu/Debian:
sudo apt-get install ntp
The current date can be viewed by the command:
date
Example of setting the time zone:
cp /usr/share/zoneinfo/Europe/Kiev /etc/localtime
timedatectl list-timezones
timedatectl list-timezones | grep -i europe
timedatectl set-timezone Europe/Kiev
Setting hours and minutes:
date -s 10:18
date --set 10:18
Example of full time setting (without spaces, in digital form):
date monthdayhourminuteyear.second
Checking the time server:
ntpdate -q SERVER
View status:
sudo ntpq -p
ntpq -c peers
Let’s start editing the configuration file /etc/ntp.conf.
A few lines:
Specify the server with which to compare the time:
server 0.ubuntu.pool.ntp.org
server 1.ubuntu.pool.ntp.org
...
We prohibit all access to the server:
restrict default ignore
Or we allow access from the internal network:
restrict 192.168.0.0 mask 255.255.255.0 nomodify notrap
Restart ntp to make the changes in the configuration file take effect:
sudo service ntp restart
An example of time synchronization from the Windows command line with a Linux server:
net time \\SERVER /set /yes
See also my articles:
IPTables rules for NTP and SNTP
Time sync on Ubuntu 18.04