[Mageia-dev] Why ntpdate still there?

Mon Feb 11 13:18:23 CET 2013

'Twas brillig, and Pierre Jarillon at 11/02/13 11:19 did gyre and gimble:
+> ntpdate is no longer necessary because ntpd includes all functions necessary 
+> to set the clock.
+> 
+> Use of ntpdate in crontab is a very bad idea because a great number of  users 
+> can make a burst of activity and a saturation of servers.
+> ntpd is more accurate with few requests and can also setup the clock.
+> ntpd makes requests after a long time. More the clock is adjusted, more it 
+> waits before a new request.
+> 
+> 
+> In man ntpdate, we can see:
+>  Disclaimer:  The functionality of this program is now available in the ntpd 
+> program. See the -q command line option in the ntpd - Network Time Protocol 
+> (NTP) daemon page. After a  suitable period of mourning, the ntpdate program 
+> is to be retired from this distribution.
+> 
+> ntpdate and ntp are active in drakxservices... IMO, this is a nonsense.
+
+ntpdate is a service that is run prior to ntpd itself. This was done
+previously to ensure the time was set correctly due to a (deliberate)
+limitation in ntpd itself which did not change the clock when large
+jumps were involved. It attempts to keep the change continuous and
+avoids large jumps.
+
+See this section from the man page:
+
+       Under ordinary conditions, ntpd slews the clock so that the time
+is effectively continuous and never runs backwards. If due to extreme
+network congestion an error spike  exceeds  the
+       step  threshold,  by  default 128 ms, the spike is discarded.
+However, if the error persists for more than the stepout threshold, by
+default 900 s, the system clock is stepped to the
+       correct value. In practice the need for a step has is extremely
+rare and almost always the result of a hardware failure. With the -x
+option the step threshold is increased to 600  s.
+       Other options are available using the tinker command on the
+Miscellaneous Options page.
+
+       The  issues  should  be carefully considered before using these
+options. The maximum slew rate possible is limited to 500
+parts-per-million (PPM) by the Unix kernel. As a result, the
+       clock can take 2000 s for each second the clock is outside the
+acceptable range. During this interval the clock will not be consistent
+with any other network  clock  and  the  system
+       cannot be used for distributed applications that require
+correctly synchronized network time.
+
+
+So ntpdate as a service is just a one-shot thing, it happens once at
+boot to ensure the clocks are properly set and then ntpd takes over for
+the rest of the time that machine stays up.
+
+As far as I'm aware, there is nothing integrated into crontab regarding
+ntpdate, but please feel free to correct me on that one.
+
+Col
+
+
+
+-- 
+
+Colin Guthrie
+colin(at)mageia.org
+http://colin.guthr.ie/
+
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+  Tribalogic Limited http://www.tribalogic.net/
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+