The HTTP Time Protocol (HTP) is used to synchronize a computer's time with web servers as reference time source. Htpdate will synchronize your computer's time by extracting timestamps from HTTP headers found in web server responses. Htpdate can be used as a daemon, to keep your computer synchronized. The accuracy of htpdate is at least -+0.5 seconds (better with multiple servers). If this is not good enough for you, try the ntpd package.
Install the htpdate package if you need tools for keeping your system's time synchronized via the HTP protocol. Htpdate works also through proxy servers.
Tested on Linux and FreeBSD only, but should work for most Unix flavors.
$ tar zxvf htpdate-x.y.z.zip
or
$ tar jxvf htpdate-x.y.z.tar.gz
$ cd htpdate-X.Y.Z
$ make
$ make install
To compile with HTTPS support, install openssl development files
$ make ENABLE_HTTPS=1
An example init script (scripts/htpdate.init) for use in /etc/init.d/ is included, but not installed automatically. This scripts will run htpdate as a daemon. There is also a service file example for systemd (scripts/htpdate.service).
Another option is to use htpdate in a cronjob and start it periodically from cron. For a daily time sync it would look something like this: 5 3 * * * /usr/bin/htpdate -s www.example.com
Usage:
htpdate [-046abdhlqstxD] [-i pid file] [-m minpoll] [-M maxpoll]
[-p precision] [-P <proxyserver>[:port]] [-u user[:group]]
<host[:port]> ...
Eg. htpdate -q www.example.com
Eg. htpdate -a -t https://www.example.com http://www.example.com
In general, if more web servers are specified, the accuracy will increase.
See manpage for more details.
Version v1.2.4 introduced https support.
This project is a fork based on htp from Eddy Vervest (http://www.vervest.org/htp). This fork exists only because I was unable to submit patches to the original project due to the lack of a public repository available.
A year after this fork, the original author opened a repository on https://github.com/twekkel/htpdate.
Use this fork if you need https support and some other fixes, use the main author project for a maintained version of the original software.