FreeBSD use the Network Time Protocol (NTP) for synchronizing the clocks of computer systems over packet-switched, variable-latency data networks. NTP uses UDP port 123. If you have one computer or single server then you can easily synchronization time with other NTP servers. All you need is ntp client called ntpdate. It is use to set the date and time via NTP servers.
FreeBSD: Install NTP Client
Use any one of the following command to install NTP:
# pkg_add -rv ntp
# cd /usr/ports/net/ntp # make; make install
Pick appropriate NTP Servers
Visit public ntp timeserver list to pick up your NTP server.
Open UDP port 123 at firewall
If you are running FreeBSD ipfilter firewall, you need to open the UDP port 123. Just add following rule to your firewall script:
pass out quick on lnc0 proto udp from YOUR-SERVER to any port = 123 keep state
pass out quick on lnc0 proto udp from YOUR-SERVER to TIME-SERVER-IP port = 123 keep state
For example, my FreeBSD workstation IP is 192.168.1.16 and 126.96.36.199 is IP of NTP server then my rule is in ipf.conf file as follows:
pass out quick on lnc0 proto udp from 192.168.1.16 to 188.8.131.52 port = 123 keep state
FreeBSD test clock synchronization
Just run ntpdate command as follows to see you can set date and clock via NTP:
Set wrong date (Mon Dec 13 4:27 pm):
# date 0412131627
Now set correct date with ntp client:
# ntpdate -v -b in.pool.ntp.org
13 Dec 16:27:50 ntpdate: ntpdate 4.2.0-a Thu Nov 3 07:34:22 UTC 2005 (1)
25 Jan 12:35:47 ntpdate: step time server 184.108.40.206 offset 35237275.965726 sec
You can verify that correct data is setup:
Wed Jan 25 12:36:21 IST 2006
Enable date and time/ clock Synchronization at boot time
You need to set ntpdate via /etc/rc.local file.
# vi /etc/rc.conf
Append following line to it:
Save and close the file. Make sure you have correct ntpdate_hosts server entry.
Updated for accuracy.