If the degree of change in your system clock is such that the list of
"potential" issues you listed below occured when running ntpdate every 12
minutes you have bigger problems and "ntpd" will not provide any solution.
--
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( Biggest security gap -- an open mouth )
`-------------------------------------'
--
Paul-Andrew Joseph Miseiko
On Mon, 12 Sep 2005, wayne wrote:
In <[EMAIL PROTECTED]> J Robinson <[EMAIL PROTECTED]> writes:
*/12 * * * * /usr/sbin/ntpdate -s timeserver1
timeserver2 timeserver3 timeserver4
By default, ntpdate sends 4 packets to each ntp server to try and get
somewhat accurate time. So, on average, you are sending one packet
every 3 minutes to each of those servers. That isn't horrible, but it
isn't very good either.
Another problem with running ntp via cron like that is that you will
send all your packets on the minute. When lots of people do this, it
means that there is a spike in usage every minute as all the packets
from these cron jobs come in at exactly the same time. This increases
the load and reduces the accuracy of the time you are getting.
I (probably mistakenly) assumed that running ntpdate
periodically would put less load on my servers than
using ntpd, and I also assumed that it wouldn't put
undue load on the ntp servers either. Is these
assumptions wrong?
Yes, your assumption is wrong.
When running well, ntpd will send one request every 1024 seconds,
about once every 15 minutes. So, what you are doing is generating
about 5 times as much load as just using ntpd.
Worse, ntpd will do a *much* better job of keeping your clock in sync
with the correct time. The ntpdate command can make the clock jump
forward or backwards if the offset is too large, which can sometimes
cause programs to do funny things. Video and music may skip or hang
for short periods, timestamps on files can get set wrong and might not
be backed up, etc. Using ntpd, your clock will run more smoothly.
-wayne
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