synctime - Synchronize clock to an atomic time reference




Synctime sets the system clock to the National Institute of Standards and Technology (NIST) Time Mark Generator Device, an atomic standard in Fort Collins, Colorado. Synctime synchronizes itself with the service, sets the system clock, and adjusts the time zone (if necessary), all during a 15 second phone call. The service is available on a three-line hunt group at (303) 494-4774. Each of the three lines has its own Time Code Generator Device linked to the NBS 9 cesium beam atomic frequency standard used as a time base at NIST.

This “atomic clock” is accurate to one second in 300,000 years. Since data sent through the phone system takes time arrive, the service employs a communications delay correction feature. This allows the received time to be accurate within milliseconds.

Synctime requires a resource file in the $/etc/rsrc directory called “synctime.rsrc”. The resource file’s format follows this example (comments are shown next to each line):

1-303/494-4774 # NIST number 1200 # Dialup speed -8 # Hour difference from UTC PST # Standard time zone PDT # Daylight savings time zone 1900 # Year 0 of this century

Time information is sent in Universal Coordinated Time (UTC) format, also known as Greenwich Mean Time (GMT), the world time at the zero meridian.

The time zone difference you enter will offset the UTC time and date received and set your clock to your local time. In places such as Newfoundland where the time difference contains a fraction of an hour, use “-3.5”. If you are in California, use “-8”. In New York, use “-5”.

The next two lines in the resource file give the three-letter time zone abbreviations for your location, starting with standard time. Some areas of the nation do not make use of daylight savings time, so enter the standard time zone abbreviation on both lines.

The last resource line holds year 0 for the current century (e.g. 1900). This value must be adjusted every 100 years. You may have to adjust it only once in your lifetime.

As synctime proceeds, it writes progress information to the console, and keeps a log of the events as they happen. (The log is mailed to “root” when synctime is done). Synctime reports the number of seconds the clock was off, the newly set time according to the atomic clock reference, and the number of days, if fewer than 50, before a daylight savings or standard time adjustment. It also updates the time zone, if necessary.


resource file,
holds current time zone abbreviation.