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HTPDATE(8) System Manager's Manual HTPDATE(8) 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 time- stamp 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). Conve- nient 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 be- tween 30 minutes and 32 hours. Htpdate calculates the optimal polling frequency between minimum and maximum values. Only ap- plicable when running in daemon mode. -n Don't use a proxy, even if the appropriate http_proxy environ- ment variable is defined. -p Precision determines the operating accuracy of htpdate. Preci- sion 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 (de- fault 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 ad- justing 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 speci- fied, but in general 3 to 5 hosts should be enough for a redun- dant 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 fol- lowing 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 2.0.0 HTPDATE(8)
NAME | SYNOPSIS | DESCRIPTION | OPTIONS | ENVIRONMENT | EXAMPLES | AUTHOR | SEE ALSO
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