OpenNTPD (part of the OpenBSD project) is a daemon that can be used to synchronize the system clock to internet time servers using the Network Time Protocol, and can also act as a time server itself if needed. It implements the Simple Network Time Protocol version 4, as described in RFC 5905, and the Network Time Protocol version 3, as described in RFC 1305.
Install the package. The default configuration is actually usable if all you want is to sync the time of the local computer.
To configure OpenNTPD, you need to edit
/etc/ntpd.conf. See for all available options.
To sync to a single particular server, uncomment and edit the "server" directive.
The "servers" directive works the same as the "server" directive, however, if the DNS name resolves to multiple IP address, ALL of them will be synced to. The default, "pool.ntp.org" is working and should be acceptable in most cases. You can find the server's URL in your area at www.pool.ntp.org/zone/@.
Any number of "server" or "servers" directives may be used.
If you want the computer you run OpenNTPD on to also be a time server, simply uncomment and edit the "listen" directive.
listen on *
will listen on all interfaces, and
listen on 127.0.0.1 listen on ::1
will only listen on the loopback interface.
Your time server will only begin to serve time after it has synchronized itself to a high resolution. This may take hours, or days, depending on the accuracy of your system.
Start OpenNTPD at boot
Making openntpd dependent upon network access
If you have intermittent network access (you roam around on a laptop, you use dial-up, etc), it does not make sense to have
openntpd running as a system daemon on start up. Here are a few ways you can control
openntpd based on the presence of a network connection.
Using NetworkManager dispatcher
OpenNTPD can be brought up/down along with a network connection through the use of NetworkManager's dispatcher scripts.
Create these two scripts and mark them executable using chmod.
#!/bin/sh systemctl start openntpd.service
#!/bin/sh systemctl stop openntpd.service
Using dhclient hooks
Another possibility is to use dhclient hooks to start and stop openntpd. When dhclient detects a change in state it will run the following scripts:
Using dhcpcd hooks
if $if_up; then systemctl start openntpd.service elif $if_down; then systemctl stop openntpd.service fi
Error adjusting time
If you find your time set incorrectly and in log you see:
openntpd adjtime failed: Invalid argument
# ntpd -s -d
This is also how you would manually sync your system.