NAME

       htpdate - Time synchronization (daemon)

SYNOPSIS

       htpdate  [-046acdhlnqstvxDF]  [-f  driftfile]  [-i  pidfile] [-m minpoll] [-M maxpoll] [-p precision] [-P
       <proxyserver>[:port]] [-u user[:group]] <URL> ...

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  using the Greenwich Mean Time (GMT) HTTP headers
       timestamp from web servers. HTTP and HTTPS are both supported.

       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, use a ntp package like ntpd, OpenNTPD
       or chrony.

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).

       -c     Verify server certificate (default no verification).

       -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.
              Multiple -d options increase verbosity. The maximum is 3.

       -f     Read/write the systematic drift of the system clock. See also -x.

       -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.

       -n     Don't use a proxy, even if the appropriate http_proxy environment variable is defined.

       -p     Precision determines the operating accuracy of htpdate. Precision specifies the  number  of  steps
              (default 4, maximum of 9) for htpdate to determine the second boundary.

       -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).

       -v     Show version.

       -x     Let htpdate compensate for the systematisch clock drift by adjusting system clock frequency.

       -D     Run as daemon. This option requires root privileges.

       -F     Run daemon in foreground. Daemon will not fork or  write  PID  file.  This  option  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   Port number (default 80 and 8080 for proxy server).

       path   Path to resource (e.g. /index.html).

ENVIRONMENT

       Htpdate supports proxies for HTTP connections. The standard way to  specify  the  proxy  location,  which
       htpdate recognizes, is using the following environment variable:

       http_proxy
           If set, the http_proxy variable should contain the URL of the proxy for HTTP connections.

EXAMPLES

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

       Request time from multiple web servers:
           htpdate www.example.com https://example.com http://example.com:80

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

       Adjust time smoothly and log output to syslog (eg. cron):
           htpdate -al www.example.com:80/htpdate.html

       HTTP/1.0 request in IPv6 literal format (RFC 2732):
           htpdate -0 [2001:db8:1af6::123]:80

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

       Run htpdate in the foreground with all output going to the terminal:
           htpdate -F www.example.com

       Read clock drift during start of htpdate and update when a new value has been established:
           htpdate -Dx -f /etc/htpdate.drift 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, OpenNTPD, chrony, adjtimex(8), ntp_adjtime,

htpdate                                           version 1.3.7                                       HTPDATE(8)