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NTP time server

Paul D. DeRocco
When I enabled more systemd journal output for some other purpose, I noticed
that I was getting occasional messages

    ntpd_intres[1644]: host name not found: time.server.example.com

I figured, oh, that's another default config file that one is supposed to
edit before the thing will actually work. It didn't take long to find
/etc/ntp.conf, which contains the following:

    # This obtains a random server which will be close
    # (in IP terms) to the machine.  Add other servers
    # as required, or change this.
    server time.server.example.com

One would think that "time.server.example.com" is just some placeholder, but
the preceding comment suggest that it is some magic name that makes the
server do something fancy. So I tried changing it to the name of a real time
server, by looking up a nearby one on the web and entering its name. Ten
minutes later, my NTP server died:

    Jan 01 10:39:48 overo systemd[1]: ntpd.service: main process exited,
code=exited, status=255/n/a
    Jan 01 10:39:48 overo systemd[1]: Unit ntpd.service entered failed state

I tried a different server and restarted the service. Same result.

When I first restarted the service, after editing the file, I got this:

    systemd[1]: Stopping Network Time Service...
    ntpd_intres[1644]: ntpd exiting on signal 15
    ntpd[1642]: ntpd exiting on signal 15
    systemd[1]: Starting Network Time Service...
    systemd[1]: PID 1642 read from file /run/ntpd.pid does not exist.
    ntpd[1790]: ntpd 4.2.6p5@1.2349 Fri Jul 19 18:43:50 UTC 2013 (2)

so obviously it knew what time it was then. It continued spewing journal
messages:

    ntpd[1791]: proto: precision = 30.517 usec
    ntpd[1791]: Listen and drop on 0 v4wildcard 0.0.0.0 UDP 123
    ntpd[1791]: Listen and drop on 1 v6wildcard :: UDP 123
    ntpd[1791]: Listen normally on 2 lo 127.0.0.1 UDP 123
    ntpd[1791]: Listen normally on 3 eth0 192.168.123.139 UDP 123
    ntpd[1791]: Listen normally on 4 lo ::1 UDP 123
    ntpd[1791]: peers refreshed
    ntpd[1791]: Listening on routing socket on fd #21 for interface updates
    systemd[1]: Started Network Time Service.
    systemctl status ntpd | more
    ntpd.service - Network Time Service
          Loaded: loaded (/lib/systemd/system/ntpd.service; enabled)
          Active: active (running) since Sat, 2000-01-01 09:58:28 UTC; 32s
ago
         Process: 1790 ExecStart=/usr/bin/ntpd -p /run/ntpd.pid
(code=exited, status=0/SUCCESS)
        Main PID: 1791 (ntpd)
          CGroup: name=systemd:/system/ntpd.service

In other words, when it finshed starting the service, it had reset the clock
to the start of 2000. Why would it do that? Doesn't the Overo have an RTC
that keeps reasonable time even in the absence of any NTP connection to the
outside world?

So is "time.server.example.com" really a code for "find me a server
automagically"? I googled that string and didn't come up with anything but a
copy of the /etc/ntp.conf file itself. If it is, then why is it outputting
error messages every ten minutes?

More to the point, am I supposed to do something with /etc/ntp.conf, or just
leave it the way it is in the standard build?

--

Ciao,               Paul D. DeRocco
Paul                mailto:[hidden email]
 


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Re: NTP time server

Andy Walls


On Wed, 2013-07-24 at 12:55 -0700, Paul D. DeRocco wrote:

> When I enabled more systemd journal output for some other purpose, I noticed
> that I was getting occasional messages
>
>     ntpd_intres[1644]: host name not found: time.server.example.com
>
> I figured, oh, that's another default config file that one is supposed to
> edit before the thing will actually work. It didn't take long to find
> /etc/ntp.conf, which contains the following:
>
>     # This obtains a random server which will be close
>     # (in IP terms) to the machine.  Add other servers
>     # as required, or change this.
>     server time.server.example.com
>
> One would think that "time.server.example.com" is just some placeholder, but
> the preceding comment suggest that it is some magic name that makes the
> server do something fancy. So I tried changing it to the name of a real time
> server, by looking up a nearby one on the web and entering its name. Ten
> minutes later, my NTP server died:
>
>     Jan 01 10:39:48 overo systemd[1]: ntpd.service: main process exited,
> code=exited, status=255/n/a
>     Jan 01 10:39:48 overo systemd[1]: Unit ntpd.service entered failed state
>
> I tried a different server and restarted the service. Same result.

ntpd will panic if the time servers have a large offset (1000 seconds)
from the local clock.  It's ntp's way of telling you, "Fix your clock,
I'm not going to guess who's right and who's wrong and what NTP epoch
we're in."

Also, if the offset is more than 4 hours, not even the -g or -q flags to
ntpd or the 'tinker panic 0' configuration line will work to set the
clock.

> When I first restarted the service, after editing the file, I got this:
>
>     systemd[1]: Stopping Network Time Service...
>     ntpd_intres[1644]: ntpd exiting on signal 15
>     ntpd[1642]: ntpd exiting on signal 15
>     systemd[1]: Starting Network Time Service...
>     systemd[1]: PID 1642 read from file /run/ntpd.pid does not exist.
>     ntpd[1790]: ntpd 4.2.6p5@1.2349 Fri Jul 19 18:43:50 UTC 2013 (2)
>
> so obviously it knew what time it was then. It continued spewing journal
> messages:

Are you sure?  Or is that the date and time ntpd was built?

>     ntpd[1791]: proto: precision = 30.517 usec
>     ntpd[1791]: Listen and drop on 0 v4wildcard 0.0.0.0 UDP 123
>     ntpd[1791]: Listen and drop on 1 v6wildcard :: UDP 123
>     ntpd[1791]: Listen normally on 2 lo 127.0.0.1 UDP 123
>     ntpd[1791]: Listen normally on 3 eth0 192.168.123.139 UDP 123
>     ntpd[1791]: Listen normally on 4 lo ::1 UDP 123
>     ntpd[1791]: peers refreshed
>     ntpd[1791]: Listening on routing socket on fd #21 for interface updates
>     systemd[1]: Started Network Time Service.
>     systemctl status ntpd | more
>     ntpd.service - Network Time Service
>           Loaded: loaded (/lib/systemd/system/ntpd.service; enabled)
>           Active: active (running) since Sat, 2000-01-01 09:58:28 UTC; 32s
> ago
>          Process: 1790 ExecStart=/usr/bin/ntpd -p /run/ntpd.pid
> (code=exited, status=0/SUCCESS)
>         Main PID: 1791 (ntpd)
>           CGroup: name=systemd:/system/ntpd.service
>
> In other words, when it finshed starting the service, it had reset the clock
> to the start of 2000. Why would it do that?

ntpd will never jump the clock by more than 4 hours, even if you tell it
a one time large jump is OK.

Comments from the Dr. Mills on the matter:
http://lists.ntp.org/pipermail/bugs/2005-August/002443.html


>  Doesn't the Overo have an RTC
> that keeps reasonable time even in the absence of any NTP connection to the
> outside world?

You need an initial proper clock setting.

If you need it automatically set after power up then you can:
1. install a battery (the Gumstix TOBI boards have a battery holder) or
2. get the correct time from another source, like a GPS, and use 'date'
or settimeofday() to set the system time.


> So is "time.server.example.com" really a code for "find me a server
> automagically"?

No.  It's probably in the default file so that millions of misconfigured
embedded devices don't DoS the time servers.

http://pages.cs.wisc.edu/~plonka/netgear-sntp/


>  I googled that string and didn't come up with anything but a
> copy of the /etc/ntp.conf file itself. If it is, then why is it outputting
> error messages every ten minutes?

If you are fielding a product with a non-user-configurable timeserver,
take a look at:
http://www.pool.ntp.org/en/vendors.html

If not, then use time.nist.gov if in the US:
http://tf.nist.gov/tf-cgi/servers.cgi


> More to the point, am I supposed to do something with /etc/ntp.conf, or just
> leave it the way it is in the standard build?

It's useless, if you leave it alone.  I also believe the line

restrict default

leaves UDP port 123 for IPv4 and IPv6 pretty wide open for external
machines to connect to your ntpd daemon using (ntpdc and ntpq) and muck
with it.

Regards,
Andy


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Re: NTP time server

Scott Ellis
This post was updated on .
Hi Andy,

> ntpd will never jump the clock by more than 4 hours, even if you tell it
> a one time large jump is OK.

I'm not doubting that is what the manual says, but on my Gumstix/Beaglebone
systems, none with battery backup and often left unpowered for days, when
they start up I always get a good system time set from ntpd (I'm assuming).

ntpd is started with the -g flag.

Example

root@duo1:/var/volatile/log# grep ntp messages
Dec 31 19:00:00 duo1 daemon.notice ntpd[601]: proto: precision = 30.517 usec
Dec 31 19:00:00 duo1 daemon.debug ntpd[601]: ntp_io: estimated max descriptors: 1024, initial socket boundary: 16
Dec 31 19:00:00 duo1 daemon.info ntpd[601]: Listen and drop on 0 v4wildcard 0.0.0.0 UDP 123
Dec 31 19:00:00 duo1 daemon.info ntpd[601]: Listen and drop on 1 v6wildcard :: UDP 123
Dec 31 19:00:00 duo1 daemon.info ntpd[601]: Listen normally on 2 lo 127.0.0.1 UDP 123
Dec 31 19:00:00 duo1 daemon.info ntpd[601]: Listen normally on 3 eth0 192.168.10.110 UDP 123
Dec 31 19:00:00 duo1 daemon.info ntpd[601]: Listen normally on 4 lo ::1 UDP 123
Dec 31 19:00:00 duo1 daemon.info ntpd[601]: peers refreshed
Dec 31 19:00:00 duo1 daemon.info ntpd[601]: Listening on routing socket on fd #21 for interface updates
Dec 31 19:00:03 duo1 daemon.info ntpd[601]: Listen normally on 5 eth0 fe80::215:c9ff:fe28:fed5 UDP 123
Dec 31 19:00:03 duo1 daemon.info ntpd[601]: peers refreshed
Dec 31 19:00:03 duo1 daemon.debug ntpd[601]: new interface(s) found: waking up resolver

root@duo1:/var/volatile/log# tail -5 messages
Dec 31 19:00:02 duo1 daemon.info avahi-daemon[617]: Service "duo1" (/services/sftp-ssh.service) successfully established.
Dec 31 19:00:03 duo1 daemon.info ntpd[601]: Listen normally on 5 eth0 fe80::215:c9ff:fe28:fed5 UDP 123
Dec 31 19:00:03 duo1 daemon.info ntpd[601]: peers refreshed
Dec 31 19:00:03 duo1 daemon.debug ntpd[601]: new interface(s) found: waking up resolver
Jul 25 09:58:18 duo1 authpriv.notice login[642]: ROOT LOGIN  on '/dev/ttyO2'

root@duo1:/var/volatile/log# date
Thu Jul 25 10:00:06 EDT 2013

root@duo1:/var/volatile/log# ps -w | grep ntpd
  601 root      3400 S    /usr/bin/ntpd -p /var/run/ntp.pid -g
  654 root      2184 S    grep ntpd

root@duo1:/var/volatile/log# cat /etc/timestamp
200001010002

It could be the ntpd daemon built from the meta-openembedded
repo has the sanity limit set to zero. The code is monstrous and I
didn't feel like wading through it.
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Re: NTP time server

Miner, Jonathan W (US SSA)


-----Original Message-----
From: Scott Ellis [mailto:[hidden email]]
Sent: Thursday, July 25, 2013 10:05 AM
To: [hidden email]
Subject: Re: [Gumstix-users] NTP time server

Hi Andy,

> ntpd will never jump the clock by more than 4 hours, even if you tell
> it a one time large jump is OK.

I'm not doubting that is what the manual says, but on my Gumstix/Beaglebone systems, none with battery backup and often left unpowered for days, when they start up I always get a good system time set from ntpd (I'm assuming).

ntpd is started with the -g flag.
-----------------------------------
According to the man page that is the expected behavior for -g

 "This option allows the time to be set to any value without restriction; however, this can happen only once."

This is similar to the practice of running ntpdate to set the clock against an known stable time source, then running ntpd to keep the clocks in sync.

- Jon

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Re: NTP time server

Ash Charles
In reply to this post by Andy Walls
Thanks Andy.

That was rather interesting reading---I now have a far better
appreciation for ntp.

So, should the gumstix repositories be setting a different default
value for the NTP server?
--Ash

On Thu, Jul 25, 2013 at 5:33 AM, Andy Walls <[hidden email]> wrote:

>
>
> On Wed, 2013-07-24 at 12:55 -0700, Paul D. DeRocco wrote:
>> When I enabled more systemd journal output for some other purpose, I noticed
>> that I was getting occasional messages
>>
>>     ntpd_intres[1644]: host name not found: time.server.example.com
>>
>> I figured, oh, that's another default config file that one is supposed to
>> edit before the thing will actually work. It didn't take long to find
>> /etc/ntp.conf, which contains the following:
>>
>>     # This obtains a random server which will be close
>>     # (in IP terms) to the machine.  Add other servers
>>     # as required, or change this.
>>     server time.server.example.com
>>
>> One would think that "time.server.example.com" is just some placeholder, but
>> the preceding comment suggest that it is some magic name that makes the
>> server do something fancy. So I tried changing it to the name of a real time
>> server, by looking up a nearby one on the web and entering its name. Ten
>> minutes later, my NTP server died:
>>
>>     Jan 01 10:39:48 overo systemd[1]: ntpd.service: main process exited,
>> code=exited, status=255/n/a
>>     Jan 01 10:39:48 overo systemd[1]: Unit ntpd.service entered failed state
>>
>> I tried a different server and restarted the service. Same result.
>
> ntpd will panic if the time servers have a large offset (1000 seconds)
> from the local clock.  It's ntp's way of telling you, "Fix your clock,
> I'm not going to guess who's right and who's wrong and what NTP epoch
> we're in."
>
> Also, if the offset is more than 4 hours, not even the -g or -q flags to
> ntpd or the 'tinker panic 0' configuration line will work to set the
> clock.
>
>> When I first restarted the service, after editing the file, I got this:
>>
>>     systemd[1]: Stopping Network Time Service...
>>     ntpd_intres[1644]: ntpd exiting on signal 15
>>     ntpd[1642]: ntpd exiting on signal 15
>>     systemd[1]: Starting Network Time Service...
>>     systemd[1]: PID 1642 read from file /run/ntpd.pid does not exist.
>>     ntpd[1790]: ntpd 4.2.6p5@1.2349 Fri Jul 19 18:43:50 UTC 2013 (2)
>>
>> so obviously it knew what time it was then. It continued spewing journal
>> messages:
>
> Are you sure?  Or is that the date and time ntpd was built?
>
>>     ntpd[1791]: proto: precision = 30.517 usec
>>     ntpd[1791]: Listen and drop on 0 v4wildcard 0.0.0.0 UDP 123
>>     ntpd[1791]: Listen and drop on 1 v6wildcard :: UDP 123
>>     ntpd[1791]: Listen normally on 2 lo 127.0.0.1 UDP 123
>>     ntpd[1791]: Listen normally on 3 eth0 192.168.123.139 UDP 123
>>     ntpd[1791]: Listen normally on 4 lo ::1 UDP 123
>>     ntpd[1791]: peers refreshed
>>     ntpd[1791]: Listening on routing socket on fd #21 for interface updates
>>     systemd[1]: Started Network Time Service.
>>     systemctl status ntpd | more
>>     ntpd.service - Network Time Service
>>           Loaded: loaded (/lib/systemd/system/ntpd.service; enabled)
>>           Active: active (running) since Sat, 2000-01-01 09:58:28 UTC; 32s
>> ago
>>          Process: 1790 ExecStart=/usr/bin/ntpd -p /run/ntpd.pid
>> (code=exited, status=0/SUCCESS)
>>         Main PID: 1791 (ntpd)
>>           CGroup: name=systemd:/system/ntpd.service
>>
>> In other words, when it finshed starting the service, it had reset the clock
>> to the start of 2000. Why would it do that?
>
> ntpd will never jump the clock by more than 4 hours, even if you tell it
> a one time large jump is OK.
>
> Comments from the Dr. Mills on the matter:
> http://lists.ntp.org/pipermail/bugs/2005-August/002443.html
>
>
>>  Doesn't the Overo have an RTC
>> that keeps reasonable time even in the absence of any NTP connection to the
>> outside world?
>
> You need an initial proper clock setting.
>
> If you need it automatically set after power up then you can:
> 1. install a battery (the Gumstix TOBI boards have a battery holder) or
> 2. get the correct time from another source, like a GPS, and use 'date'
> or settimeofday() to set the system time.
>
>
>> So is "time.server.example.com" really a code for "find me a server
>> automagically"?
>
> No.  It's probably in the default file so that millions of misconfigured
> embedded devices don't DoS the time servers.
>
> http://pages.cs.wisc.edu/~plonka/netgear-sntp/
>
>
>>  I googled that string and didn't come up with anything but a
>> copy of the /etc/ntp.conf file itself. If it is, then why is it outputting
>> error messages every ten minutes?
>
> If you are fielding a product with a non-user-configurable timeserver,
> take a look at:
> http://www.pool.ntp.org/en/vendors.html
>
> If not, then use time.nist.gov if in the US:
> http://tf.nist.gov/tf-cgi/servers.cgi
>
>
>> More to the point, am I supposed to do something with /etc/ntp.conf, or just
>> leave it the way it is in the standard build?
>
> It's useless, if you leave it alone.  I also believe the line
>
> restrict default
>
> leaves UDP port 123 for IPv4 and IPv6 pretty wide open for external
> machines to connect to your ntpd daemon using (ntpdc and ntpq) and muck
> with it.
>
> Regards,
> Andy
>
>
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Re: NTP time server

Scott Ellis
I've been using this ntp.conf taken from the Raspbian distro

--- ntp.conf ---

# /etc/ntp.conf, configuration for ntpd; see ntp.conf(5) for help

driftfile /var/lib/ntp/ntp.drift


# Enable this if you want statistics to be logged.
#statsdir /var/log/ntpstats/

statistics loopstats peerstats clockstats
filegen loopstats file loopstats type day enable
filegen peerstats file peerstats type day enable
filegen clockstats file clockstats type day enable


# pool.ntp.org maps to about 1000 low-stratum NTP servers.  Your server will
# pick a different set every time it starts up.  Please consider joining the
# pool: <http://www.pool.ntp.org/join.html>
server 0.debian.pool.ntp.org iburst
server 1.debian.pool.ntp.org iburst
server 2.debian.pool.ntp.org iburst
server 3.debian.pool.ntp.org iburst


# Access control configuration; see /usr/share/doc/ntp-doc/html/accopt.html for
# details.  The web page <http://support.ntp.org/bin/view/Support/AccessRestrictions>
# might also be helpful.
#
# Note that "restrict" applies to both servers and clients, so a configuration
# that might be intended to block requests from certain clients could also end
# up blocking replies from your own upstream servers.

# By default, exchange time with everybody, but don't allow configuration.
restrict -4 default kod notrap nomodify nopeer noquery
restrict -6 default kod notrap nomodify nopeer noquery

# Local users may interrogate the ntp server more closely.
restrict 127.0.0.1
restrict ::1

# Clients from this (example!) subnet have unlimited access, but only if
# cryptographically authenticated.
#restrict 192.168.123.0 mask 255.255.255.0 notrust


# If you want to provide time to your local subnet, change the next line.
# (Again, the address is an example only.)
#broadcast 192.168.123.255

# If you want to listen to time broadcasts on your local subnet, de-comment the
# next lines.  Please do this only if you trust everybody on the network!
#disable auth
#broadcastclient

--- end ntp.conf ---

But I run sysvinit systems. It may need tweaking for systemd systems.
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Re: NTP time server

Paul D. DeRocco
In reply to this post by Andy Walls
> From: Andy Walls [mailto:[hidden email]]
>
> ntpd will never jump the clock by more than 4 hours, even if
> you tell it
> a one time large jump is OK.
>
> Comments from the Dr. Mills on the matter:
> http://lists.ntp.org/pipermail/bugs/2005-August/002443.html

Your explanation seems to match the reality. I've configured in the
pool.dtp.org addresses (this is a prototype at this point), and everything
seems to be fine.

--

Ciao,               Paul D. DeRocco
Paul                mailto:[hidden email]


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Re: NTP time server

Andy Walls
In reply to this post by Scott Ellis
Hi Scott,

On Thu, 2013-07-25 at 07:05 -0700, Scott Ellis wrote:

> Hi Andy,
>
> > ntpd will never jump the clock by more than 4 hours, even if you tell it
> > a one time large jump is OK.
>
> I'm not doubting that is what the manual says, but on my Gumstix/Beaglebone
> systems, none with battery backup and often left unpowered for days, when
> they start up I always get a good system time set from ntpd (I'm assuming).
>
> ntpd is started with the -g flag.

Argh.  Then I need to go back and take a harder look when using a sane
reference clock peer.


My problem was that I'm running gpsd locally as my preferred (and only
non-PPS) reference clock peer, and my unit starts up with system time at
1 Jan 2000.

So when gpsd starts reporting time to ntpd, the reports from gpsd via
the shared memory clock driver have this:

        reftime   = UTC from GPS (which is the correct time)
        recvdtime = system clock (which is 13 years in the past)

ntpd looks at that mess and rejects the gpsd reference clock peer.  I
tracked it down to the clocktime() function in ntpd and its 4 hour
window restriction.


My fix was to write a small gpsd client that runs at start up that
monitors for when gpsd has its first stable fix.  It then set the system
clock using settimeofday(), upon which gpsd will make sane reports to
ntpd. (I still need to test it.)

Regards,
Andy


 


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Re: NTP time server

Andy Walls
In reply to this post by Ash Charles
Hi Ash:

On Thu, 2013-07-25 at 08:37 -0700, Ash Charles wrote:
> Thanks Andy.
>
> That was rather interesting reading---I now have a far better
> appreciation for ntp.
>
> So, should the gumstix repositories be setting a different default
> value for the NTP server?
> --Ash

Not necessarily.  You just want to make the system integrator think
about it, before ntpd tries to connect to real servers.

Having it broken out of the box, fits the bill. :)

Regards,
Andy


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Re: NTP time server

Ash Charles
On Thu, Jul 25, 2013 at 9:49 AM, Andy Walls <[hidden email]> wrote:
> Not necessarily.  You just want to make the system integrator think
> about it, before ntpd tries to connect to real servers.
>
> Having it broken out of the box, fits the bill. :)
I guess that is a point.
Does anyone know what other projects are doing on this front?  Perhaps
a yocto or gumstix vendor zone?
--ash

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