Section 26. Enable Automatic Time Synchronization (NTP)

26. Enable Automatic Time Synchronization (NTP)

BEFORE YOU BEGIN

25 Set the Time and Date

28 Dial Up to the Internet with a Modem (PPP)

30 Configure Networking Manually

SEE ALSO

97 Create an iCal Event

107 Adjust the Format of Numbers and Other Notations

139 Schedule Automatic Software Updates

The Network Time Protocol (NTP) allows your computer to keep its date and time in sync with a central server. If you have a network connectioneven an intermittent one, as you might with a laptopit's absolutely better all around to use network time rather than manually setting the system's time and date. Network time synchronizes your computer's clock (both the date and the time) with a public NTP server. Whenever your computer's network or Internet connection is active, it communicates with the NTP server to ensure that its clock is accurate; if there is any discrepancy, Mac OS X makes the adjustments automatically. Because this checking takes place in the background, the adjustments to be made are never large enough for you to noticeunless it's been a long time since your connection was active and your system clock has drifted a lot.

26. Enable Automatic Time Synchronization (NTP)

NOTE

Some computers' clocks have severe drift problems. If you find that you have to manually set your clock more than once every couple of monthsin other words, if your Mac's clock drifts by more than a couple of minutes a monthyou should consider having it serviced and getting the clock chip or CMOS/PRAM battery replaced .

KEY TERM

Network Time Protocol (NTP) A technology in which a computer (such as a Mac) can periodically check with any of a number of central, public servers and receive an accurate reading of the current time. The computer can then calibrate its clock to match the central server, which is often of military precision.

A lot of NTP servers are active on the Internet, run by organizations such as the U.S. Naval Observatory and various universities. However, Apple runs its own NTP servers as well, in various places around the world, one of which is bound to be close to your location.

1.	Open the Date & Time Preferences Open the System Preferences from the Apple menu; click Date & Time to open the Date & Time Preferences . Alternatively, select Open Date & Time from the menu that appears when you click the time display at the far right of the system's menu bar. NOTE The Clock tab is used to customize the menu bar clock display, including whether the clock should be shown in the menu bar or in a floating window, and what format the time display should take. You can even set Mac OS X to announce the time in a voice of your choosing. For more options on how the system should display the time, such as whether to use a leading zero for the hour or how noon and midnight should be represented (as variously used in different countries ), click Open International at the bottom of the screen. See 107 Adjust the Format of Numbers and Other Notations for more.
2.	Enable NTP Select the Set Date & Time Automatically check box to enable network time synchronization.
3.	Select a Time Server The default time server is time.apple.com, located at the Apple campus in Cupertino, California. There are other choices availabletime.asia.apple.com for Asia, and time.euro.apple.com for Europethat you might want to choose instead if you're not in the Americas. Because NTP operates by a carefully timed exchange of data packets, it's important to choose a time server that's geographically near to you to minimize network latency during the sync process. If you want to use a different time server (such as tick.usno.navy.mil , the United States Naval Observatory's public NTP server), enter its hostname in the input box. As soon as you select a time server, the time is synchronized; you can then close the window, because no further configuration is needed, and no changes need to be saved.