Re: [CentOS] Chrony

[Anand Buddhdev]

On 08/05/2020 13:46, Jerry Geis wrote:

Hi Jerry,


I just happened to notice this morning in /var/log/messages:

chronyd[1299]: Selected source 207.244.103.95

host 207.244.103.95
95.103.244.207.in-addr.arpa domain name pointer
dns-e.wdc-us.hosts.301-moved.de.

Just curious why my machine in Indiana (USA) is asking for time in Germany.
Wouldn't it use something closer ?


Lesson #1: do NOT take PTR records at face value. They can be wrong.

Lesson #2: in this case, look again. The company may be German, but the 
host chrony selected appears to be in the USA (wdc-us).


If you look up this IP address in RIPE NCC RIPEStat service, you'll see 
that it also geolocates to USA:


https://stat.ripe.net/207.244.103.95

Geolocation isn't perfect either, but the combination of "wdc-us", the 
Geolocation data, the fact that this IP address block was allocated by 
ARIN, and that your chrony selected it, all point to the fact the NTP 
server is in fact, close to you.


Regards,
Anand Buddhdev
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[CentOS] Chrony

[Jerry Geis]

I just happened to notice this morning in /var/log/messages:

chronyd[1299]: Selected source 207.244.103.95

host 207.244.103.95
95.103.244.207.in-addr.arpa domain name pointer
dns-e.wdc-us.hosts.301-moved.de.

Just curious why my machine in Indiana (USA) is asking for time in Germany.
Wouldn't it use something closer ?
Thanks,

jerry
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Re: [CentOS] Chrony vd NTP

[Louis Lagendijk]

On Sun, 2017-02-05 at 12:30 -0500, Robert Moskowitz wrote:
> 
> On 02/05/2017 11:58 AM, J Martin Rushton wrote:
> > On 05/02/17 16:15, Richard wrote:
> > > > Date: Sunday, February 05, 2017 10:26:05 -0500
> > > > From: Robert Moskowitz 
> > > > 
> > > > I have read:
> > > > http://thegeekdiary.com/centos-rhel-7-chrony-vs-ntp-differences
> > > > -bet
> > > > ween-ntpd-and-chronyd/
> > > > 
> > > > My server is up all the time and will serve time to internal
> > > > systems (via DHCP options).
> > > > 
> > > > Caveat is that my server is an armv7 (Cubieboard2) which does
> > > > not
> > > > have an RTC (no battery).  So whenever the system boots, the
> > > > time
> > > > is ZERO (Dec 31, 1969 or some such).
> > > > 
> > > > Chrony fixes this really fast; shortly after boot the time is
> > > > good.
> > > > Chrony CAN be configed as an internal time server.  But chrony
> > > > does
> > > > not seem to step the clock for any adjustments needed.  It is
> > > > more
> > > > important that this systems time be right all the time than to
> > > > avoid clock steps.
> > > > 
> > > > This brings me back to NTP, which normally takes hours to bring
> > > > the
> > > > time from ZERO to current, but keeps the time correct.
> > > > 
> > > > So:
> > > > 
> > > > Can Chrony check the time, say once a day?
> > > > 
> > > > Or can NTP make a BIG time jump all at once (on system
> > > > restart)?
> > > 
> > > Where I have somewhat similar issues, I have historically used a
> > > crontab "@reboot" entry to call ntpdate which gets the clock set
> > > correctly. From there ntp keeps it in sync.
> > > 
> > > This can now be accomplished with ntpd, and ntpdate is threatened
> > > with depreciation/retirement. See the top of the ntpdate man page
> > > for
> > > more details.
> > > 
> > 
> > The NTP configuration option you may be after is "tinker panic 0"
> > which
> > allows NTP to make big jumps as often as required.  See
> > ntp_misc(5).
> > There is a related discussion with making VMs take big jumps at
> > https://www.centos.org/forums/viewtopic.php?f=16=61186=258254#p
> > 258254
> 
> Thanks.  I will look at this.  All I was seeing was to use burst and 
> iburst, but they would not make the really big jump needed after
> boot.
> 
> 
With NTP you could use the ntpdate.service as well as/ before 
ntpd.service. the  former is supposed to set the clock once BEFORE ntpd
is started. 
See: https://access.redhat.com/documentation/en-US/Red_Hat_Enterprise_L
inux/6/html/Deployment_Guide/s1-Configure_ntpdate_Servers.html
Ntpdate seems to work on RHEL/Centos 7 as well...

/Louis

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Re: [CentOS] Chrony vd NTP

[Robert Moskowitz]

On 02/05/2017 11:58 AM, J Martin Rushton wrote:

On 05/02/17 16:15, Richard wrote:

Date: Sunday, February 05, 2017 10:26:05 -0500
From: Robert Moskowitz 

I have read:
http://thegeekdiary.com/centos-rhel-7-chrony-vs-ntp-differences-bet
ween-ntpd-and-chronyd/

My server is up all the time and will serve time to internal
systems (via DHCP options).

Caveat is that my server is an armv7 (Cubieboard2) which does not
have an RTC (no battery).  So whenever the system boots, the time
is ZERO (Dec 31, 1969 or some such).

Chrony fixes this really fast; shortly after boot the time is good.
Chrony CAN be configed as an internal time server.  But chrony does
not seem to step the clock for any adjustments needed.  It is more
important that this systems time be right all the time than to
avoid clock steps.

This brings me back to NTP, which normally takes hours to bring the
time from ZERO to current, but keeps the time correct.

So:

Can Chrony check the time, say once a day?

Or can NTP make a BIG time jump all at once (on system restart)?

Where I have somewhat similar issues, I have historically used a
crontab "@reboot" entry to call ntpdate which gets the clock set
correctly. From there ntp keeps it in sync.

This can now be accomplished with ntpd, and ntpdate is threatened
with depreciation/retirement. See the top of the ntpdate man page for
more details.


The NTP configuration option you may be after is "tinker panic 0" which
allows NTP to make big jumps as often as required.  See ntp_misc(5).
There is a related discussion with making VMs take big jumps at
https://www.centos.org/forums/viewtopic.php?f=16=61186=258254#p258254


So, if I understand the man page, this command should be the first one 
in /etc/ntp.conf



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Re: [CentOS] Chrony vd NTP

[Robert Moskowitz]

On 02/05/2017 11:58 AM, J Martin Rushton wrote:

On 05/02/17 16:15, Richard wrote:

Date: Sunday, February 05, 2017 10:26:05 -0500
From: Robert Moskowitz 

I have read:
http://thegeekdiary.com/centos-rhel-7-chrony-vs-ntp-differences-bet
ween-ntpd-and-chronyd/

My server is up all the time and will serve time to internal
systems (via DHCP options).

Caveat is that my server is an armv7 (Cubieboard2) which does not
have an RTC (no battery).  So whenever the system boots, the time
is ZERO (Dec 31, 1969 or some such).

Chrony fixes this really fast; shortly after boot the time is good.
Chrony CAN be configed as an internal time server.  But chrony does
not seem to step the clock for any adjustments needed.  It is more
important that this systems time be right all the time than to
avoid clock steps.

This brings me back to NTP, which normally takes hours to bring the
time from ZERO to current, but keeps the time correct.

So:

Can Chrony check the time, say once a day?

Or can NTP make a BIG time jump all at once (on system restart)?

Where I have somewhat similar issues, I have historically used a
crontab "@reboot" entry to call ntpdate which gets the clock set
correctly. From there ntp keeps it in sync.

This can now be accomplished with ntpd, and ntpdate is threatened
with depreciation/retirement. See the top of the ntpdate man page for
more details.


The NTP configuration option you may be after is "tinker panic 0" which
allows NTP to make big jumps as often as required.  See ntp_misc(5).
There is a related discussion with making VMs take big jumps at
https://www.centos.org/forums/viewtopic.php?f=16=61186=258254#p258254


Thanks.  I will look at this.  All I was seeing was to use burst and 
iburst, but they would not make the really big jump needed after boot.



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Re: [CentOS] Chrony vd NTP

[J Martin Rushton]

On 05/02/17 16:15, Richard wrote:
> 
>> Date: Sunday, February 05, 2017 10:26:05 -0500
>> From: Robert Moskowitz 
>>
>> I have read:
>> http://thegeekdiary.com/centos-rhel-7-chrony-vs-ntp-differences-bet
>> ween-ntpd-and-chronyd/
>>
>> My server is up all the time and will serve time to internal
>> systems (via DHCP options).
>>
>> Caveat is that my server is an armv7 (Cubieboard2) which does not
>> have an RTC (no battery).  So whenever the system boots, the time
>> is ZERO (Dec 31, 1969 or some such).
>>
>> Chrony fixes this really fast; shortly after boot the time is good.
>> Chrony CAN be configed as an internal time server.  But chrony does
>> not seem to step the clock for any adjustments needed.  It is more
>> important that this systems time be right all the time than to
>> avoid clock steps.
>>
>> This brings me back to NTP, which normally takes hours to bring the
>> time from ZERO to current, but keeps the time correct.
>>
>> So:
>>
>> Can Chrony check the time, say once a day?
>>
>> Or can NTP make a BIG time jump all at once (on system restart)?
> 
> Where I have somewhat similar issues, I have historically used a
> crontab "@reboot" entry to call ntpdate which gets the clock set
> correctly. From there ntp keeps it in sync.
> 
> This can now be accomplished with ntpd, and ntpdate is threatened
> with depreciation/retirement. See the top of the ntpdate man page for
> more details.
> 
The NTP configuration option you may be after is "tinker panic 0" which
allows NTP to make big jumps as often as required.  See ntp_misc(5).
There is a related discussion with making VMs take big jumps at
https://www.centos.org/forums/viewtopic.php?f=16=61186=258254#p258254



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