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31 votes
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What is NTP dispersion and how do I control it?

I see some confusion going on in the answers here. For starters, ntpclient, at least in -s mode, isn't acting as a full NTP client, it's only sending and receiving one packet, so there's no "last 8 ...
hobbs's user avatar
  • 566
25 votes
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NTP Service Auto-Discovery

You can specify an NTP server via DHCP, or Group Policy, or DNS SRV records. DHCP: GPO: SRV Record: If your client is unable to leverage any of those mechanisms... you can also pretty safely ...
Ryan Ries's user avatar
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23 votes
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Things to consider when running public NTP servers

Firstly, good for you; it's a helpful and public-spirited thing to do. That said, and given your clarification that you're planning on creating one or more DMZ VMs which will sync to and make ...
MadHatter's user avatar
  • 80.7k
17 votes

How to override the ntp information sent by dhcp in debian?

Not directly answering the question but that may come in handy. DHCP behavior On Debian (at least) the DHCP client is overriding the existing ntp service configuration. It is controlled by the ...
user5994461's user avatar
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15 votes
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How to set up local ntp server without internet access on ubuntu?

Don't do this. Seriously. Just don't. People keep coming up with the idea that NTP is designed to allow a bunch of machines all to have the same time. It isn't. It's designed, quite carefully, to ...
MadHatter's user avatar
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15 votes
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Getting gpsd address for ntpd

It seems that the loopback ip-address range 127.127.0.0/16 is used by NTPD to represent drivers for specific clocks. The third octet is the number of the specific driver as found on the list of ...
HBruijn's user avatar
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14 votes

What is NTP dispersion and how do I control it?

Just a partial answer for "What is dispersion?": A typical NTP round trip: client | | server t1 |------->| t2 t3 |<-------| t4 This yields two values, offset (the time ...
Sven's user avatar
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12 votes

Things to consider when running public NTP servers

Firstly, congrats on an NTP question that is non-facepalm material. :-) I've included some graphs at the bottom of this post to give you a feel for things. The VM in question is set to 100 Mbps in ...
Paul Gear's user avatar
  • 4,507
12 votes

Sync ntp immediately at boot with undiciplined clock

You can use the -g parameter. From the manpage: -g Normally, ntpd exits with a message to the system log if the offset exceeds the panic threshold, which is 1000 s by default. This option allows the ...
basekat's user avatar
  • 456
10 votes
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How can I synchronize system time with a NTP server continuously?

No. It is good practice to run ntpd, because that is what it is for - to continuously keep your time as precisely sync'ed to correct time as possible, with the assistance of one or more reference ...
MadHatter's user avatar
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10 votes

ntp.conf pool vs server directives

The answer was given by mboehn. To clarify more: See the document he mentioned. Especially the last lines: The pool scheme is configured using one or more pool commands with DNS names indicating ...
Woftor's user avatar
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10 votes
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ntpd synchronizes but chronyd fails

The difference is that chronyd by default uses a random source port for each client request. If the firewall doesn't allow client requests from other ports than 123, you will need to specify the port ...
mlichvar's user avatar
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9 votes
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NTP server architecture

Depending on how critical time keeping is in your environment, you may not want server1 to be a single point of failure. If you have to take it offline for maintenance or repair for an extended period ...
Aaron Copley's user avatar
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9 votes

Ntpd on local network - Preventing clock drift causing high offsets

A driftfile records the frequency of the local clock, and is a good thing to have to accurately discipline it. Ubuntu /etc/ntp.conf has a driftfile by default. Appending iburst to the server line ...
John Mahowald's user avatar
9 votes
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ntpd fails to sync TIME_ERROR: 0x41: Clock Unsynchronized

Your clock is syncing fine. The sync_ntp in your ntpq -c sysinfo proves that. The kernel messages you're referring to are transient during ntpd startup and are not anything to be worried about. The ...
Paul Gear's user avatar
  • 4,507
7 votes

Different offset in "ntpq -p" and "ntpdate -q"

ntpq outputs offset in milliseconds. ntpdate offset is in seconds. Your offset is therefore 209.956 ms vs. 0.207451 sec which is pretty close (209ms vs. 207ms)
LHWizard's user avatar
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7 votes

What is NTP dispersion and how do I control it?

Your dispersion and skew are enormous, there is a very large offset from the local clock to that peer. You should compare the offsets with the local date and set the clock manually. Get ntpd running ...
John Mahowald's user avatar
6 votes

Turn OFF NTPD immediatly synchronization

By default, ntpd will step (instead of slew) the time if the offset is greater than 128ms. You can avoid that with the -x command line option, but beware: Correcting one second of offset will take ...
Sven's user avatar
  • 99.6k
6 votes

What is NTP dispersion and how do I control it?

According to the this cisco documentation, "dispersion, reported in seconds, is the maximum clock time difference that was ever observed between the local clock and server clock". With ntp servers ...
Hagen von Eitzen's user avatar
6 votes
Accepted

Do I need ntpd on a LAMP server?

A typical single LAMP doesn't usually need a full-blown NTP server - to keep your time accurate add a ntpd -q job to run every day. You need an NTP server when more accurate time synchronization is ...
Anubioz's user avatar
  • 3,725
6 votes

NTP server architecture

While it's not strictly true that 2 servers is no use, the NTP Best Current Practices RFC (8633) recommends 4 as a minimum. NTP's intersection algorithm doesn't depend merely on quorum in the number ...
Paul Gear's user avatar
  • 4,507
6 votes

Sync ntp immediately at boot with undiciplined clock

In addition to the -g flag described above, you should add iburst to the server line on the clients. This will cause them to sync more quickly to the server. However, you can't expect your server ...
Paul Gear's user avatar
  • 4,507
5 votes

Getting gpsd address for ntpd

All IPv4 addresses in the 127/8 netblock are reserved for host loopback. However, only 127.0.0.1 is commonly used. RFC 5735, section 3. 127.0.0.0/8 - This block is assigned for use as the Internet ...
user's user avatar
  • 4,455
5 votes
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Where can I see ntpd working status (log or message)

The definitive statement is in your ntpq -c rv output, where it says stratum=3 You are sync'ed; ntpd is working. When your daemon reports a stratum that isn't 16, you know you are sync'ed. In this ...
MadHatter's user avatar
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5 votes
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NTP doesn't seem to be enabled and synchronised in Debian Jessie

To enable time synchronization with timedatectl use the command as follows. timedatectl set-ntp true This will enable the systemd service systemd-timesyncd.service. From man timedatectl. set-ntp [...
Thomas's user avatar
  • 4,305
5 votes

Ntpd on local network - Preventing clock drift causing high offsets

Your lack of a relation between your NTP server's clock time and the real-world UTC time could be the root of your problem. If your NTP server does not have multiple real-world sources (regardless of ...
Paul Gear's user avatar
  • 4,507
4 votes

Is it possible to run ntpd with a time that is intentionally distinct from system time?

The question is why would you want to do this? NTP is designed to ensure systems have the correct time (usualy within milliseconds of atomic clocks). It is possible but not recommended. You can use ...
BillThor's user avatar
  • 28k
4 votes

Why is ntpd not updating the time on my server?

If ntpd wouldn't be able to connect with the remote server, you wouldn't see an offset for that server. If ntpq would be blocked by ntpd, you would see a clear error message from ntpq. If some other ...
Robert's user avatar
  • 41
4 votes
Accepted

Is it possible to check NTPd status on a Busybox system?

BusyBox does not provide the IPC/RPC interfaces that are needed to query the status of a running BusyBox NTP daemon, so even if you install one of the mentioned query utilities they will not be able ...
mikewse's user avatar
  • 156
4 votes
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Which server will ntpd daemon prefer for time synchronization if we have multiple servers in ntp.conf file

I read that ntp use all the servers for time synchronization. Yes. Use at least 4 where feasible. A better performing one is picked as the system peer, according to the selection algorithm. Including ...
John Mahowald's user avatar

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