[ntp:questions] Re: ntpd, boot time, and hot plugging
brad at stop.mail-abuse.org
Sun Feb 6 03:07:36 UTC 2005
At 10:52 PM -0200 2005-02-04, Alain wrote:
> ntpdate with 5 servers 3 seconds
> ntpdate with 8 servers 4 seconds
> It looks like ntpdate does most things in parelel.
No, it does them in sequence. Witness:
# /usr/bin/time -p ntpdate -b 10.0.1.240 time.euro.apple.com
de.pool.ntp.org fr.pool.ntp.org nl.pool.ntp.org uk.pool.ntp.org
0.europe.pool.ntp.org 1.europe.pool.ntp.org 2.europe.pool.ntp.org
Looking for host 10.0.1.240 and service ntp
host found : 10.0.1.240
Looking for host time.euro.apple.com and service ntp
host found : interweb.euro.apple.com
Looking for host de.pool.ntp.org and service ntp
host found : ipx10540.ipxserver.de
Looking for host fr.pool.ntp.org and service ntp
host found : granny.lievin.net
Looking for host nl.pool.ntp.org and service ntp
host found : i157107.upc-i.chello.nl
Looking for host uk.pool.ntp.org and service ntp
host found : cheddar.halon.org.uk
Looking for host 0.europe.pool.ntp.org and service ntp
host found : time.as-computer.biz
Looking for host 1.europe.pool.ntp.org and service ntp
host found : change2linux.com
Looking for host 2.europe.pool.ntp.org and service ntp
host found : 184.108.40.206
Looking for host europe.pool.ntp.org and service ntp
host found : aszlig.net
6 Feb 04:05:36 ntpdate: sendto(10.0.1.240): Host is down
6 Feb 04:05:37 ntpdate: sendto(10.0.1.240): Host is down
6 Feb 04:05:38 ntpdate: sendto(10.0.1.240): Host is down
6 Feb 04:05:39 ntpdate: sendto(10.0.1.240): Host is down
6 Feb 04:05:40 ntpdate: step time server 220.127.116.11
offset -0.013175 sec
And here's ntpd:
# /usr/bin/time -p ntpd -gq -f /var/run/ntp.drift -p
ntpd: time slew -0.009592s
It just so happens that, in many cases, you can get those few
packets out to the servers and back quickly enough that ntpdate will
finish within a few seconds.
Steve has shown that ntpd will get up and running in about seven
seconds on his machine, whereas it's a bit slower on mine since some
of the servers I've selected in my ntp.conf are down/non-responsive.
I'm also on a slow ADSL line, I'm connected to that through an Apple
Airport Extreme base station on a wireless 802.11b network with WEP
encryption (which always slows down wireless network throughput), and
I'm running on an ancient PowerBook G3 laptop running MacOS X that is
being pushed fairly hard to just run the OS and keep a few programs
in memory, much less do anything useful.
Contrariwise, Steve is running on a Soekris 4801 single board
computer which is pretty much otherwise unloaded (except for ntpd),
running a fairly stripped version of FreeBSD, and I believe he's
connected to his cable modem line directly via 10/100 Base-T/TX
Ethernet as opposed to WLAN.
I don't know how much of my slow down is due to what factors, but
I'm not too surprised.
Brad Knowles, <brad at stop.mail-abuse.org>
"Those who would give up essential Liberty, to purchase a little
temporary Safety, deserve neither Liberty nor Safety."
-- Benjamin Franklin (1706-1790), reply of the Pennsylvania
Assembly to the Governor, November 11, 1755
SAGE member since 1995. See <http://www.sage.org/> for more info.
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