November 2004
Beginner
580 pages
12h 51m
English
Content preview from Linux CookbookBecome an O’Reilly member and get unlimited access to this title plus top books and audiobooks from O’Reilly and nearly 200 top publishers, thousands of courses curated by job role, 150+ live events each month,
O’Reilly covers everything we've got, with content to help us build a world-class technology community, upgrade the capabilities and competencies of our teams, and improve overall team performance as well as their engagement.I wanted to learn C and C++, but it didn't click for me until I picked up an O'Reilly book. When I went on the O’Reilly platform, I was astonished to find all the books there, plus live events and sandboxes so you could play around with the technology.I’ve been on the O’Reilly platform for more than eight years. I use a couple of learning platforms, but I'm on O'Reilly more than anybody else. When you're there, you start learning. I'm never disappointed.I'm always learning. So when I got on to O'Reilly, I was like a kid in a candy store. There are playlists. There are answers. There's on-demand training. It's worth its weight in gold, in terms of what it allows me to do.
Chapter 19. Keeping Time with NTP
Introduction
Keeping accurate time on a single PC, or on a LAN, is important for a number of reasons: maintaining accurate timestamps in logs, keeping databases happy, and ensuring that batch jobs and other automated processes run at the right times. Even more important than keeping precisely correct time is keeping all of your servers and workstations synchronized with each other.
Linux includes a motley collection of time and date utilities: ntpdate, hwclock.sh, date, 822-date, tzselect, tzsetup, vcstime, uptime, zdump, ddate, rdate, ctime, and doubtless several more. In olden times, we ran hwclock.sh, rdate, or ntpdate at boottime, or put them in cron jobs for periodic updating. ntp —the Network Time Protocol—replaces all of that. It is best to disable any of the other utilities that are set to run automatically, whether from rc*.d files or cron, and let ntp be your sole timekeeper. With one exception: ntpdate is still useful for making large corrections. If your system time is off by more than 20 or 30 minutes, ntp will take several hours, or even days, to correct it, whereas ntpdate takes care of large corrections instantly.
The command ntpd -g is supposed to replace ntpdate , but it doesn’t work well for corrections of more than an hour. If your system time is off by several hours, the ntp documentation tells you to correct it manually. If that works for you, fine; in this chapter, we’ll cover how to make the computer do the work.
ntp is implemented ...
Become an O’Reilly member and get unlimited access to this title plus top books and audiobooks from O’Reilly and nearly 200 top publishers, thousands of courses curated by job role, 150+ live events each month,
and much more.
Read now
Unlock full access
More than 5,000 organizations count on O’Reilly
O’Reilly covers everything we've got, with content to help us build a world-class technology community, upgrade the capabilities and competencies of our teams, and improve overall team performance as well as their engagement.Julian F.
I wanted to learn C and C++, but it didn't click for me until I picked up an O'Reilly book. When I went on the O’Reilly platform, I was astonished to find all the books there, plus live events and sandboxes so you could play around with the technology.Addison B.
I’ve been on the O’Reilly platform for more than eight years. I use a couple of learning platforms, but I'm on O'Reilly more than anybody else. When you're there, you start learning. I'm never disappointed.Amir M.
I'm always learning. So when I got on to O'Reilly, I was like a kid in a candy store. There are playlists. There are answers. There's on-demand training. It's worth its weight in gold, in terms of what it allows me to do.