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Time Protocol

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This is an old revision of this page, as edited by 130.89.167.52 (talk) at 04:57, 29 February 2012 (Added note about timestamp overflow, and the fact that few distros today ship an rdate utility anymore.). The present address (URL) is a permanent link to this revision, which may differ significantly from the current revision.
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The Time Protocol is a network protocol in the Internet Protocol Suite defined in 1983 in RFC 868. Its purpose is to provide a site-independent, machine readable date and time.

The Time Protocol may be implemented over the Transmission Control Protocol (TCP) or the User Datagram Protocol (UDP). A host connects to a server that supports the Time Protocol on port 37. The server then sends the time as a 32-bit unsigned integer in binary format and in network byte order, representing the number of seconds since 00:00 (midnight) 1 January, 1900 GMT, and closes the connection. Operation over UDP requires the sending of any datagram to the server port, as there is no connection setup for UDP.

Using a fixed 32-bit data format means that the timestamp counter will periodically roll over. This occurs roughly every 136 years, with the first such occurence on 7 February 2036. Programs that use the Time Protocol must have been carefully designed to use context-dependent information to distinguish these dates from those in 1900, or they might report an incorrect date and time when used after this date.

Traditionally many Unix-like operating systems used the Time Protocol to monitor and/or synchronize the clocks of different systems using the rdate utility, but today this functionality has been superseded by the Network Time Protocol (NTP) and the corresponding ntpdate utility, which report times with greater (sub-second) accuracy.

Inetd implementation

On most UNIX-like operating systems a Time Protocol server is built into the inetd (or xinetd) daemon. The service is usually not enabled by default. It may be enabled by adding the following lines to the file /etc/inetd.conf 

time   stream  tcp     nowait  root    internal
time   dgram   udp     wait    root    internal

and reloading the configuration.

See also

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