NAME

       htpdate - Time synchronization (daemon)

SYNOPSIS

       htpdate [-046abdhlqstxD] [-i pid file] [-m minpoll] [-M maxpoll] [-p precision] [-P <proxyserver>[:port]]
       [-u user[:group]] <host[:port]> ...

DESCRIPTION

       The  HTTP Time Protocol (HTP) is used to synchronize a computer's time with web servers as reference time
       source. Htp will synchronize your computer's time to Greenwich Mean Time (GMT) via HTTP headers from  web
       servers.   The  htpdate  package includes a program for retrieving the date and time from remote machines
       via a network. Htpdate works through proxy servers. Accuracy  of  htpdate  will  be  usually  within  0.5
       seconds (better with multiple servers). If this is not good enough for you, try the ntpd package.

OPTIONS

       -0     HTTP/1.0 request (default is HTTP/1.1).

       -4     Force IPv4 name resolution only. Default behaviour is to try IPv6 first and fall back to IPv4.

       -6     Force IPv6 name resolution only.

       -a     Adjust time smoothly (default in daemon mode).

       -b     Burst mode uses multiple polls for each web server to enhance accuracy.

       -d     Turn  debug on. Shows the "raw" timestamp, round trip time, time delta and and basic statistics of
              web server responses. Useful to determining the quality of a specific web server as time source.

       -h     Show help.

       -i     Set the pid file (default /var/run/htpdate.pid).

       -l     Use syslog for output (levels LOG_WARNING and LOG_INFO). Convenient if you use htpdate from cron.

       -m -M  These options specify the minimum (-m) and maximum (-M) polling intervals  for  HTP  requests,  in
              seconds.  The  default  range  is  between 30 minutes and 32 hours. Htpdate calculates the optimal
              polling frequency between minimum and maximum values. Only applicable when running in daemon mode.

       -p     Precision (in milliseconds) specifies the operating accuracy of htpdate. Internally htpdate uses a
              different algorithm to detect a time offset, when  precision  is  specified.  Precision  only  has
              effect in daemon mode. Use with caution.

       -q     Query web server and display time, but do not change time (default in interactive mode).

       -s     Set time immediate. In daemon mode -s only applies the first poll.

       -t     Turn  off  sanity  time  check.  By  default a time offset larger than a year, compared to current
              localtime, is rejected. With -t set, any time stamp will be accepted.

       -u     Set the user and group that the server normally runs at (default is root).

       -x     Let htpdate compensate for the systematisch clock drift.

       -D     Run as daemon (requires root privileges).

       -P     Proxy server hostname or ip-address.

       host   Web server hostname or ip-address. Up to 16 hosts may be specified, but in general 3  to  5  hosts
              should be enough for a redundant and accurate setup.

       port   Portnumber (default 80 and 8080 for proxy server)

EXAMPLES

       Request time from web server (don't update local clock):
              htpdate -q www.example.com

       Verbose output (don't update local clock):
              htpdate -d -q www.example.com

       Adjust time smoothly and log output to syslog (eg. cron):
              htpdate -a -l www.example.com

       HTTP/1.0 request in IPv6 literal format (RFC 2732):
              htpdate -0 [2001:DB8:1af6::123]:80

       Run htpdate as daemon:
              htpdate -D www.example.com

       Daemon mode for the security minded:
              htpdate -D -u nobody:nogroup www.example.com

AUTHOR

       Eddy Vervest <eddy@vervest.org>, http://www.vervest.org/htp

SEE ALSO

       rdate, timed, ntpd, adjtimex, ntp_adjtime,
       HTP implementation by Roy Keene (http://www.rkeene.org/oss/htp/)

htpdate                                           version 1.2.2                                       HTPDATE(8)