The Clock Mini-HOWTO: Introduction

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The real-time-clock chips used on PC motherboards (and even expensive workstations) are notoriously inaccurate. Linux provides a simple way to correct for this in software, making the clock potentially *very* accurate even without an external time source. But most people don’t seem to know about it, for several reasons:

  1. It’s not mentioned in most of the general « how to set up linux » documentation, and it would be difficult to set up automatically at install time (although not impossible in theory, if you have a modem).
  2. If you check « man clock » you’ll get clock(3), which is not what you want. (try « man 8 clock »).
  3. Most people don’t seem to care what time it is anyway.
  4. Those few who do care often want to use the xntpd package from louie.udel.edu to sync to an external time source, such as a network time server or radio clock.

This mini-HOWTO describes the low-tech approach. If you’re at all interested in this sort of thing, I highly recommend that you spend some time at http://www.eecis.udel.edu/~ntp/ which includes all kinds of interesting stuff, including complete info on xntpd and links to NIST and USNO (I have a few more comments on xntpd at the end.)

Note

If you run more than one OS on your machine, you should only let one of them reset the CMOS clock, so they don’t confuse each other. If you regularly run both Linux and Windows on the same machine, you may want to check out some of the shareware clock programs that are available for Windows instead (follow the links from the URL above).

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