Re: [gentoo-user] /etc/init.d/: ntpd or ntp-client?

[Alan McKinnon]

On Wednesday 04 February 2009 15:38:11 Stroller wrote:
> Before I do any investigation, can someone tell me if my understanding  
> so far is correct? Is ntpd supposed to keep the machine's clock in  
> constant sync, or is it only (say) a server to offer the date to  
> clients? (depending upon the clock being set correctly by other means)  
> I thought I had configured ntpd with upstream servers separately from  
> ntp-client.

ntp is one of those things that looks really easy and turns out to be 
horrendously complicated once you scratch the surface. The problem is not ntp 
itself, it's the subject of time.

ntp is indeed both a server for it's host machine and your LAN, but also a 
client to upstream. It is also full of precautions:

It will not make your clock jump forwards or backwards if your time is way 
out. ntp keeps track of how weak your clock spring is and gradually pulls the 
local clock back into sync with the master clock by making the length of 
seconds fractionally shorter or longer. It does this so that there are no 
gaps in the time record. If it suddenly pulled the clock forward, the time 
tick for midnight might never happen and your crons might not run. I forget 
what the threshold is, but it's not long; and it can take several hours to 
correct a clock that is only a few minutes out.

ntpd is really designed for Unix servers with 3 digit uptimes and clocks not 
assembled by Mickey Mouse's younger brother (which seems to include all pcs 
ever made.....)

Most folk are better off with ntpdate run from a cron. When run, it checks the 
upstream time and immediately corrects the local clock to that time. Schedule 
it for once an hour or so, depending on your bandwidth and local ntp site's 
policies.

-- 
alan dot mckinnon at gmail dot com