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• What units does the ntp drift file use?

  - by arielf

  When the ntpd daemon is running, the file: /var/lib/ntp/ntp.drift gets updated periodically. Example: 17:20 hostname 118 ~> ls -l /var/lib/ntp/ntp.drift -rw-r--r-- 1 ntp ntp 7 May 20 16:46 /var/lib/ntp/ntp.drift # So it looks like it was last updated ~34 minutes ago The file has one number in it, for example, looking at a 4 virtual hosts, I find these values, respectively: -22.086 -10.214 -13.669 6.045 I assume these are seconds per day(?), but not sure. man ntpd mentions a different drift file /etc/ntp.drift which doesn't seem to exist. The man page doesn't explain what units are being used for the drift. Questions: Is /etc/ntp.drift actually /var/lib/ntp/ntp.drift on Ubuntu? What units is the drift expressed in? Thanks!

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• Delay NTP Initialisation, Cisco 877W, IOS 12.4(24)T1

  - by Mike Insch

  I have a Cisco 877W which I'm using for my home ADSL connection (and as a refresher in Cisco IOS). I've got a working config in-place with my PPPoA connection coming online correctly, and VLANs and other settings configured as I want them, but I can't crack the NTP configuration. For NTP, I have the following defined ntp server 0.uk.pool.ntp.org source Dialer0 ntp server 1.uk.pool.ntp.org source Dialer0 ntp server 2.uk.pool.ntp.org source Dialer0 ntp server 3.uk.pool.ntp.org source Dialer0 This setup works fine when issued in Global Configuration Mode when the Dialer0 interface (ATM0.1) is up. The configuration fails at startup though: Translating "1.uk.pool.ntp.org"...domain server (208.67.222.222) (208.67.220.220) ntp server 1.uk.pool.ntp.org source Dialer0 ^ % Invalid input detected at "^" marker. This is repeated for the other servers defined. Obviously the DNS lookup for the server(s) fails because the DNS servers cannot be accessed because the external interface is not yet online. Is there a way to delay the NTP configuration until afte the Dialer0 interface is fully initialised? Can the NTP commands be triggered by the Line Protocol on the Dialer0 interface transitioning to the up state? Alternatively, can the NTP commands be delayed for 5 minutes after the router has finished initialising? Any advice, or pointers to useful documentation or examples gratefully received ...

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• Ubuntu NTP issues

  - by Anups

  I am trying to setup the NTP server on Ubuntu machine. Am breaking my head in this particular issue. Getting an error ntpdate[5005]: no server suitable for synchronization found when doing the command ntppdate. Can anyone please help me out in this? /etc/ntp.conf: server 0.ubuntu.pool.ntp.org server 1.ubuntu.pool.ntp.org server 2.ubuntu.pool.ntp.org server 3.ubuntu.pool.ntp.org Also when I gave command netstat -anltp | grep "LISTEN" tcp 0 0 127.0.0.1:53 0.0.0.0:* LISTEN 1816/dnsmasq tcp 0 0 0.0.0.0:22 0.0.0.0:* LISTEN 939/sshd tcp 0 0 127.0.0.1:631 0.0.0.0:* LISTEN 1013/cupsd tcp 0 0 127.0.0.1:39558 0.0.0.0:* LISTEN 5529/rsession tcp 0 0 0.0.0.0:902 0.0.0.0:* LISTEN 1275/vmware-authdla tcp 0 0 127.0.0.1:47304 0.0.0.0:* LISTEN 5822/rsession tcp6 0 0 :::80 :::* LISTEN 1400/apache2 tcp6 0 0 :::22 :::* LISTEN 939/sshd tcp6 0 0 ::1:631 :::* LISTEN 1013/cupsd So what should I do so that it listens on 123? If I get output as PORT STATE SERVICE 123/udp open ntp If I give command nmap -p 123 -sU -P0 192.168.36.198, it means UDP is open right? Then why doesn't it show in the command to to show listening ports?

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• NTP configuration in NEXUS Switch

  - by Pandi Durai

  i'm planning to change the NTP peer to 172.29.100.44,but i'm unable to delete the existing and add new peer NTP peer IP in Nexus switch,Please suggest me in removing the existing configuration. i have use the below commands to remove the peer,But still its not getting deleated from running configuration.Even if i add new peer,its not getting reflecting in running configuration. no ntp peer 172.29.100.10 use-vrf management. ntp peer 172.29.100.44 use-vrf management Existing configuration: ntp distribute. ntp peer 172.29.100.10 use-vrf management. ntp source-interface mgmt0. ntp commit. My another nexus is working fine with the below Configuration: ntp peer 172.29.100.10 use-vrf management. ntp peer 172.29.100.44 use-vrf management. ntp source-interface mgmt0.

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• How to force a clock update using ntp?

  - by ysap

  I am running Ubuntu on an ARM based embedded system that lacks a battery backed RTC. The wake-up time is somewhere during 1970. Thus, I use the NTP service to update the time to the current time. I added the following line to /etc/rc.local file: sudo ntpdate -s time.nist.gov However, after startup, it still takes a couple of minutes until the time is updated, during which period I cannot work effectively with tar and make. How can I force a clock update at any given time? UPDATE 1: The following (thanks to Eric and Stephan) works fine from command line, but fails to update the clock when put in /etc/rc.local: $ date ; sudo service ntp stop ; sudo ntpdate -s time.nist.gov ; sudo service ntp start ; date Thu Jan 1 00:00:58 UTC 1970 * Stopping NTP server ntpd [ OK ] * Starting NTP server [ OK ] Thu Feb 14 18:52:21 UTC 2013 What am I doing wrong? UPDATE 2: I tried following the few suggestions that came in response to the 1st update, but nothing seems to actually do the job as required. Here's what I tried: Replace the server to us.pool.ntp.org Use explicit paths to the programs Remove the ntp service altogether and leave just sudo ntpdate ... in rc.local Remove the sudo from the above command in rc.local Using the above, the machine still starts at 1970. However, when doing this from command line once logged in (via ssh), the clock gets updated as soon as I invoke ntpdate. Last thing I did was to remove that from rc.local and place a call to ntpdate in my .bashrc file. This does update the clock as expected, and I get the true current time once the command prompt is available. However, this means that if the machine is turned on and no user is logged in, then the time never gets updates. I can, of course, reinstall the ntp service so at least the clock is updated within a few minutes from startup, but then we're back at square 1. So, is there a reason why placing the ntpdate command in rc.local does not perform the required task, while doing so in .bashrc works fine?

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• NTP service, offset increasing after sync

  - by Ajay

  I have installed Ubuntu 12.10 version on my PC. I am running NTP service having NTP server as GPS. I found that when we start NTP service by ntp start command, PC is able to sync with GPS as i get '*' symbol before GPS IP when i run ntpq -p command. This remains good for some time and then the * symbol is removed which means that PC is not synchronized to that server. Now, by running command ntpq -p it shows that all parameter are OK but as '*' is removed, slowly offset goes on increasing. remote refid st t when poll reach delay offset jitter ============================================================================== *192.168.100.33 .GPS. 1 u 7 16 1 2.333 23.799 0.808 remote refid st t when poll reach delay offset jitter ============================================================================== *192.168.100.33 .GPS. 1 u 14 16 3 2.333 23.799 0.879 remote refid st t when poll reach delay offset jitter ============================================================================== *192.168.100.33 .GPS. 1 u 11 16 7 2.333 23.799 1.500 remote refid st t when poll reach delay offset jitter ============================================================================== *192.168.100.33 .GPS. 1 u 8 16 17 2.333 23.799 2.177 below are the last 4 ntp status when sync is lost with GPS ============================================================================== 192.168.100.33 .GPS. 1 u 1 16 377 2.404 1169.94 1.735 remote refid st t when poll reach delay offset jitter ============================================================================== 192.168.100.33 .GPS. 1 u - 16 377 2.513 1171.80 0.898 remote refid st t when poll reach delay offset jitter ============================================================================== 192.168.100.33 .GPS. 1 u 15 16 377 2.513 1171.80 0.898 Since, GPS is already available, PC never re-synchronize itself to GPS later ON. I have to restart the ntp service and then PC synchronizes to GPS and '*' symbol arrives.

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• Troubleshooting unwanted NTP Traffic

  - by Jaxaeon

  A domain controller running Windows Server 2012 is sending NTP and NETBIOS traffic to an address that has never been configured as a time provider. The server logs give no indication that any NTP traffic is failing. The only place I see any evidence of this traffic is in pfSense system logs: (Blocked) Jun 9 08:48:50 DOMAIN 10.0.1.100:123 192.128.127.254:123 UDP (Blocked) Jun 9 08:48:53 DOMAIN 10.0.1.100:137 192.128.127.254:137 UDP As far as I can tell the NTP service is working normally otherwise: DC2.domain.com[10.0.1.101:123]: ICMP: 0ms delay NTP: -0.0131705s offset from DC1.domain.com RefID: DC1.domain.com [10.0.1.100] Stratum: 3 DC1.domain.com *** PDC ***[10.0.1.100:123]: ICMP: 0ms delay NTP: +0.0000000s offset from DC1.domain.com RefID: clock1.albyny.inoc.net [64.246.132.14] Stratum: 2 The time provider NtpClient is currently receiving valid time data from 1.pool.ntp.org,0×1 (ntp.m|0x0|0.0.0.0:123->204.2.134.163:123). The time provider NtpClient is currently receiving valid time data from 0.pool.ntp.org,0×1 (ntp.m|0x0|0.0.0.0:123->64.246.132.14:123). The time service is now synchronizing the system time with the time source 0.pool.ntp.org,0×1 (ntp.m|0x0|0.0.0.0:123->64.246.132.14:123). I've been inside and out of the NTP configuration and cannot find any reason for this traffic. Reverse DNS points the destination address to nothing.attdns.com. pinging nothing.attdns.com from the domain controller in question leads to a response from loopback (127.0.0.2) which makes my head hurt. Any ideas? EDIT1: It should probably be noted that after a dns flush, nslookup 192.128.127.254 returns nothing.attdns.com. 192.128.127.254 is not present in domain.com DNS records. The attdns.com domain is not present in cached lookups. 127.in-addr.arpa is clean of any funkyness. EDIT2: The loopback ping response from nothing.attdns.com is possibly unrelated. Machines on other networks are also displaying this behavior. EDIT3: As mentioned in the comments, I tracked the problem network adapter back to my pfSense VM hosted in esxi 5.5 (I know shame on me for virtualizing a firewall). pfSense was configured to use DC1.domain.com as its primary time provider, but upon changing it back to pool.ntp.org the problem persists. pfSense logs give no indication of NTP misconfiguration. Everywhere I can think to look this VM is identified as 10.0.1.253, so I still have no idea why it’s sending NTP requests as 192.128… Since this firewall was a temporary solution to a problem that no longer exists so I am going to decommission it. EDIT4: The queries were coming from another machine sharing the same virtual adapter as the firewall. The machine has two local adapters: one for LAN, and the other for attached hardware that uses an Ethernet connection. That hardware sits in the the mystery subnet, and the machine is broadcasting NTP requests over both adapters.

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• Replacing sick NTP server source and re-synching (with internal time currently 2 minutes late)

  - by l0c0b0x

  One of the external NTP servers (the primary one--currently) we're using as source seems to not be responding to NTP calls. Unfortunately, on our core router (Cisco 6509), the NTP functionality hasn't switched to the secondary NTP external server as it was expected. As a result, our core router which is pretty much our main internal NTP source is 2 minutes late. I'm planning to fix the external router issue by making the external NTP source be the one currently working. I'm wondering, how much will a 2 minute change affect my users and services? Specially since these days, we're heavily relying on certificate-based authentication. We're a Windows/Cisco shop. Internal NTP setup: [Core Router 1 / Cisco 6509]: looking out to two external NTP servers (in which the primary one is not responding to NTP calls) [Core Router 2]: Synching with Core router 1 (primary), working external router (secondary) [Other Cisco network devices]: Synching with Core router 1 (primary), core router 2 (secondary) [Domain controller(s)]: Synching with Core router 1 [All windows clients/servers]: Synching with domain controllers

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• Access to NTP via IP which doesn't change often

  - by faulty

  I'm trying to sync the clock of our production server located in a data center with pool.ntp.org. For security reason, our servers has no internet access unless we requested to open specific ip/port explicitly. I worked out a list of IPs based on 0.asia.ntp.org 1.asia.ntp.org 2.asia.ntp.org 3.asia.ntp.org Not realizing ntp.org is using round robin DNS and the servers being voluntary, they changes from time to time. In fact the IP I've got from 3.asia.ntp.org last month is no longer working now. I'm wondering if there's a publicly known NTP server that doesn't change as often or if there's a way to go around this without having to request an update to the firewall on a monthly basis. I believe many admin is facing the same issue here.

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• High Jitter in NTP and poll value never goes above 128

  - by Aseem

  I have a lot of servers syncing to the same NTP servers (4). Not every server is in the same LAN. Some are 3 hops away from the NTP servers and some are 6 hops away. On couple of servers I see that the poll value never touches the 1024 mark and the jitter value is in double digits. Could it be due to the system hardware? These are windows servers (physical) and require as accurate time as possible. Please advice what I should do. Some of the stats that I collected manually from the bad box (which is 6 hops away from the ntp servers) C:\Program Files (x86)\NTP>ntpq -p -n remote refid st t when poll reach delay offset jitter ============================================================================== +*.*.*.25 *.*.*.233 2 u 12 128 377 1.210 -12.579 14.913 +*.*.*.26 *.*.*.233 2 u 96 128 377 1.067 -2.235 9.885 **.*.*.27 *.*.*.233 2 u 24 128 377 1.038 -7.569 11.178 +*.*.*.28 *.*.*.233 2 u 49 128 377 1.288 -11.058 14.544 remote refid st t when poll reach delay offset jitter ============================================================================== +*.*.*.25 *.*.*.233 2 u 124 128 377 0.614 -6.212 5.329 +*.*.*.26 *.*.*.233 2 u 93 128 377 0.910 -9.431 3.111 +*.*.*.27 *.*.*.233 2 u 1 128 377 0.824 -7.428 3.129 **.*.*.28 *.*.*.233 2 u 84 128 377 1.503 -8.230 3.511 remote refid st t when poll reach delay offset jitter ============================================================================== **.*.*.25 *.*.*.233 2 u 117 128 377 1.235 -4.084 11.405 +*.*.*.26 *.*.*.233 2 u 96 128 377 1.335 -11.813 13.130 +*.*.*.27 *.*.*.233 2 u 130 128 377 1.549 -14.036 16.381 -*.*.*.28 *.*.*.233 2 u 79 128 377 1.258 13.395 22.203 remote refid st t when poll reach delay offset jitter ============================================================================== **.*.*.25 *.*.*.233 2 u 88 128 377 1.235 -4.084 14.068 +*.*.*.26 *.*.*.233 2 u 63 128 377 1.335 -11.813 17.086 +*.*.*.27 *.*.*.233 2 u 103 128 377 1.549 -14.036 20.691 -*.*.*.28 *.*.*.233 2 u 47 128 377 1.258 13.395 20.231 remote refid st t when poll reach delay offset jitter ============================================================================== +*.*.*.25 *.*.*.233 2 u 47 64 377 0.652 -15.805 14.077 **.*.*.26 *.*.*.233 2 u 11 64 377 1.013 -14.423 11.375 -*.*.*.27 *.*.*.233 2 u 63 64 377 0.765 -2.030 7.680 +*.*.*.28 *.*.*.233 2 u 4 64 377 1.191 -17.980 14.393 remote refid st t when poll reach delay offset jitter ============================================================================== -*.*.*.25 *.*.*.233 2 u 3 128 377 1.576 18.665 21.999 +*.*.*.26 *.*.*.233 2 u 73 128 377 0.637 -5.012 14.405 **.*.*.27 *.*.*.233 2 u 127 128 377 0.272 -8.237 14.438 +*.*.*.28 *.*.*.233 2 u 123 128 377 1.190 -14.383 18.875 C:\Program Files (x86)\NTP>ntpdc -c loopinfo offset: -0.016430 s frequency: 7.106 ppm poll adjust: 18 watchdog timer: 133 s offset: -0.016430 s frequency: 7.106 ppm poll adjust: 18 watchdog timer: 341 s offset: -0.000149 s frequency: 6.645 ppm poll adjust: 0 watchdog timer: 383 s offset: 0.015735 s frequency: 6.725 ppm poll adjust: 7 watchdog timer: 577 s offset: -0.010331 s frequency: 6.748 ppm poll adjust: 21 watchdog timer: 567 s offset: -0.009427 s frequency: 6.687 ppm poll adjust: 28 watchdog timer: 301 s offset: -0.007361 s frequency: 6.612 ppm poll adjust: 30 watchdog timer: 155 s offset: -0.008106 s frequency: 4.358 ppm poll adjust: 30 watchdog timer: 291 s NTP.conf # NTP configuration file # Use drift file driftfile "C:\Program Files (x86)\NTP\ntp.drift" # Logs statistics loopstats peerstats clockstats statsdir "C:\Program Files (x86)\NTP\logs\" # directory for statistics files filegen peerstats file peerstats type day enable filegen loopstats file loopstats type day enable filegen clockstats file clockstats type day enable logfile "C:\Program Files (x86)\NTP\logs\syslog.txt" # Use specific NTP servers server *.*.*.25 minpoll 4 maxpoll 7 iburst server *.*.*.26 minpoll 4 maxpoll 7 iburst server *.*.*.27 minpoll 4 maxpoll 7 iburst server *.*.*.28 minpoll 4 maxpoll 7 iburst

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• Cisco ASA5505 won't sync with NTP

  - by Martijn Heemels

  Today I noticed that the clock my Cisco ASA 5505 firewall was running about 15 minutes late, which surprised me since I've set up the NTP client. My two NTP servers 10.10.0.1 and 10.10.0.2 are virtualized Windows Server 2008 R2 domain controllers, and both have the correct time. As shown below, the ASA knows about the two servers, can ping them and seems to poll them periodically, so I suppose it can reach them both. The ASA claims its time source is NTP, however the clock is unsynchronized. Neither host is marked as synced. Result of the command: "ping 10.10.0.1" Type escape sequence to abort. Sending 5, 100-byte ICMP Echos to 10.10.0.1, timeout is 2 seconds: !!!!! Success rate is 100 percent (5/5), round-trip min/avg/max = 1/1/1 ms Result of the command: "sh ntp ass" address ref clock st when poll reach delay offset disp ~10.10.0.1 .LOCL. 1 78 1024 377 0.5 643.69 17.0 ~10.10.0.2 10.10.0.1 2 190 1024 377 0.9 655.91 58.4 * master (synced), # master (unsynced), + selected, - candidate, ~ configured Result of the command: "sh ntp stat" Clock is unsynchronized, stratum 16, no reference clock nominal freq is 99.9984 Hz, actual freq is 99.9984 Hz, precision is 2**6 reference time is 00000000.00000000 (07:28:16.000 CEST Thu Feb 7 2036) clock offset is 0.0000 msec, root delay is 0.00 msec root dispersion is 0.00 msec, peer dispersion is 0.00 msec Result of the command: "sh clock detail" 10:33:23.769 CEDT Tue Jun 26 2012 Time source is NTP UTC time is: 08:33:23 UTC Tue Jun 26 2012 Summer time starts 02:00:00 CEST Sun Mar 25 2012 Summer time ends 03:00:00 CEDT Sun Oct 28 2012 I've tried the basic steps of manually setting the time and removing and adding the timeservers, to no avail. My ASA's ntp config is simply: ntp server 10.10.0.1 ntp server 10.10.0.2 Do I need to enable authentication to use a Windows NTP server? Any thoughts?

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• enable/disable ntp service on ubuntu 12.04

  - by ntphelp

  Our application runs on Ubuntu 12.04 Precise. On this server, we have both ntpdate and ntp. How to enable and disable the NTP service on-demand? I tried # sudo update-rc.d -f ntp remove/default and # sudo update-rc.d ntp enable/disable commands, but when I reboot server the ntp service starts running! I suspect ntpdate is starting ntp service on reboot. I removed ntpdate package from one of my experimental server, then ntp didn't start on reboot after issuing: # update-rc.d ntp disable Is there a way to control this? or is there way to permanently disable ntpdate?

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• Problems setting NTP sever with w32tm for a DC that is a Hyper-V guest

  - by R.Tonheim

  Hello ! I have tried to sett my DC to get its time from several NTP severs. I follow this answer (http://serverfault.com/questions/24298/w32time-sync-problems-for-hyper-v-guests-w32time-event-ids-38-24-29-35/24299#24299) to do it. First I disable Time Synchronization in the Hyper-V Integration Services for each guest. Then restart the Windows Time serviceon the guest. I had before this used this command: w32tm /config /manualpeerlist:"ntp.uio.no;timekeeper. uio.no;nissen.uio.no;0.no.pool.ntp.org;1.no.pool.ntp.org;2.no.pool.ntp.org" /syn cfromflags:manual /reliable:yes /update And the cmd sad: The command completed successfully. But the time was still 10 min wrong... I run w32tm again after restarted the DC without it having any effect. The w32tm /query /status still say: "Source: Local CMOS Clock" FROM MY CMD: Microsoft Windows [Version 6.0.6002] Copyright (c) 2006 Microsoft Corporation. All rights reserved. C:\Users\Administrator.MHGw32tm /query /status Leap Indicator: 0(no warning) Stratum: 1 (primary reference - syncd by radio clock) Precision: -6 (15.625ms per tick) Root Delay: 0.0000000s Root Dispersion: 10.0000000s ReferenceId: 0x4C4F434C (source name: "LOCL") Last Successful Sync Time: 05.09.2009 20:06:21 Source: Local CMOS Clock Poll Interval: 6 (64s) C:\Users\Administrator.MHGw32tm /config /manualpeerlist:"ntp.uio.no;timekeeper. uio.no;nissen.uio.no;0.no.pool.ntp.org;1.no.pool.ntp.org;2.no.pool.ntp.org" /syn cfromflags:manual /reliable:yes /update The command completed successfully. C:\Users\Administrator.MHGw32tm /query /status Leap Indicator: 0(no warning) Stratum: 1 (primary reference - syncd by radio clock) Precision: -6 (15.625ms per tick) Root Delay: 0.0000000s Root Dispersion: 10.0000000s ReferenceId: 0x4C4F434C (source name: "LOCL") Last Successful Sync Time: 05.09.2009 20:06:21 Source: Local CMOS Clock Poll Interval: 6 (64s) C:\Users\Administrator.MHG

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• How do NTP Servers Manage to Stay so Accurate?

  - by Akemi Iwaya

  Many of us have had the occasional problem with our computers and other devices retaining accurate time settings, but a quick sync with an NTP server makes all well again. But if our own devices can lose accuracy, how do NTP servers manage to stay so accurate? Today’s Question & Answer session comes to us courtesy of SuperUser—a subdivision of Stack Exchange, a community-driven grouping of Q&A web sites. Photo courtesy of LEOL30 (Flickr). The Question SuperUser reader Frank Thornton wants to know how NTP servers are able to remain so accurate: I have noticed that on my servers and other machines, the clocks always drift so that they have to sync up to remain accurate. How do the NTP server clocks keep from drifting and always remain so accurate? How do the NTP servers manage to remain so accurate? The Answer SuperUser contributor Michael Kjorling has the answer for us: NTP servers rely on highly accurate clocks for precision timekeeping. A common time source for central NTP servers are atomic clocks, or GPS receivers (remember that GPS satellites have atomic clocks onboard). These clocks are defined as accurate since they provide a highly exact time reference. There is nothing magical about GPS or atomic clocks that make them tell you exactly what time it is. Because of how atomic clocks work, they are simply very good at, having once been told what time it is, keeping accurate time (since the second is defined in terms of atomic effects). In fact, it is worth noting that GPS time is distinct from the UTC that we are more used to seeing. These atomic clocks are in turn synchronized against International Atomic Time or TAI in order to not only accurately tell the passage of time, but also the time. Once you have an exact time on one system connected to a network like the Internet, it is a matter of protocol engineering enabling transfer of precise times between hosts over an unreliable network. In this regard a Stratum 2 (or farther from the actual time source) NTP server is no different from your desktop system syncing against a set of NTP servers. By the time you have a few accurate times (as obtained from NTP servers or elsewhere) and know the rate of advancement of your local clock (which is easy to determine), you can calculate your local clock’s drift rate relative to the “believed accurate” passage of time. Once locked in, this value can then be used to continuously adjust the local clock to make it report values very close to the accurate passage of time, even if the local real-time clock itself is highly inaccurate. As long as your local clock is not highly erratic, this should allow keeping accurate time for some time even if your upstream time source becomes unavailable for any reason. Some NTP client implementations (probably most ntpd daemon or system service implementations) do this, and others (like ntpd’s companion ntpdate which simply sets the clock once) do not. This is commonly referred to as a drift file because it persistently stores a measure of clock drift, but strictly speaking it does not have to be stored as a specific file on disk. In NTP, Stratum 0 is by definition an accurate time source. Stratum 1 is a system that uses a Stratum 0 time source as its time source (and is thus slightly less accurate than the Stratum 0 time source). Stratum 2 again is slightly less accurate than Stratum 1 because it is syncing its time against the Stratum 1 source and so on. In practice, this loss of accuracy is so small that it is completely negligible in all but the most extreme of cases. Have something to add to the explanation? Sound off in the comments. Want to read more answers from other tech-savvy Stack Exchange users? Check out the full discussion thread here.

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• Local or public NTP servers?

  - by BeeOnRope

  For a relatively large network (thousands of hosts) - what are the arguments for and against running a locally managed (pool of) NTP server(s) (perhaps periodically set via some public NTP server) and having all other hosts on the network use that (pool of) NTP server(s) versus having all hosts simply use public NTP servers directly, say via ntp.pool.org? Aside from the pros and cons, What is typical best practice today?

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• Securing NTP: which method to use?

  - by Harry

  Can someone good at NTP configuration please share which method is the best/easiest to implement a secure, tamper-proof version of NTP? Here are some difficulties... I don't have the luxury of having my own stratum 0 time source, so must rely on external time servers. Should I read up on the AutoKey method or should I try to go the MD5 route? Based on what I know about symmetric cryptography, it seems that the MD5 method relies on a pre-agreed set of keys (symmetric cryptography) between the client and the server, and, so, is prone to man-in-the-middle attack. AutoKey, on the other hand, does not appear to work behind a NAT or a masquerading host. Is this still true, by the way? (This reference link is dated 2004, so I'm not sure what is the state of art today.) 4.1 Are public AutoKey-talking time servers available? I browsed through the NTP book by David Mills. The book looks excellent in a way (coming from the NTP creator after all), but the information therein is also overwhelming. I just need to first configure a secure version of NTP and then may be later worry about its architectural and engineering underpinnings. Can someone please wade me through these drowning NTP waters? Don't necessarily need a working config from you, just info on which NTP mode/config to try and may be also a public time server that supports that mode/config. Many thanks, /HS

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• Time jumping forward on NTP failure

  - by Dan

  I have been having some weird problems with NTP for a while. If I use ntpdate to set the time then it sets fine. ntpd then invariably fails to find a server (I have loads configured) and decides to set the clock forward about 5 hours. It's a Xen server with dom0 set to a different timezone so I'm not sure if that is interfering with it. How can I make sure I ignore the dom0 time and have ntpd not change the time if it fails to reach a time server? EDIT: I now do not think it is ntpd giving me problems, I turned ntpd off and it jumped forward seemingly randomly.

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• Hosting an NTP server on a standalone network

  - by cdated

  I have a LAN that is not connected to the internet, and I am trying to sychronize all the machines, Windows and Linux, to an NTP. All I've been able to find is setting up an NTP client with an internet NTP. How can I setup my own Linux NTP server, or find good documentation on how?

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• NTP doesn't sync

  - by Jonathan

  I'm using Meinberg NTP to sync the time in a VPS. The clock refuses to sync - there's a ~30s shift comparing to other servers. Meinberg NTP comes with a status script that checks hte delay\jitter every 10s and it is showing all zeros. Actions I've taken which didn't help: Restarted the NTP service using a script that comes with Meinberg NTP Added port 123 for UDP and TCP as an exception port to Windows Firewall Added Meinberk NTP executables as an exception program to Windows Firewall validated iburst appears after each server listed in the configuration file Restarted the server The OS is a Windows Server Standard SP2 32bit. What did I miss?

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• Windows clients not using NTP server provided via DHCP

  - by gencha

  I have a network consisting mostly of Windows Vista and 7 clients and an Ubuntu server. The server provides both the DHCP and NTP services through dhcp3-server and openntpd. In my dhcpd.conf, the subnet is declared as follows: subnet 10.10.10.0 netmask 255.255.255.0 { range 10.10.10.10 10.10.10.200; option broadcast-address 10.10.10.255; option routers 10.10.10.1; option ntp-servers 10.10.10.1; } The clients don't seem to be using the NTP server though. When I capture the network traffic with Wireshark during the DHCP process, I also see no mention of the NTP option in the DHCP offer message. I am not quite sure if the clients would have to specifically request that option to receive it or if I have to make another configuration to offer the option.

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• periodically overridding NTP for simulation purposes

  - by Gerard

  I have this situation: NTP is used to sync time on a set of Windows 7 and Server 2008 machines. Nothing out of the ordinary about this. periodically on this system, the time needs to be changed for testing/training purposes (it is a training simulation system that has a lot of time-dependent operations). My question: As NTP in general does not really like big time jumps or changes AFAIK, is there a standard way this could be set up to allow the clock to be changed at the root NTP server in the system and have it propagate through the system in a reasonable amount of time (a minute or two?) It is not acceptable to disable and/or restart all NTP client services to achieve this. Any ideas? It would be nice to do this without writing some kind of custom script to disable services and update clocks all over the place. Thanks in advance.

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• Looking for a NTP Server Software for Windows

  - by Simon

  I'm looking for a, preferably free, NTP Server for Windows Server 2003/2008. We have already tried the built in Windows Time Server, but our tests did show that it is not very accurate, we see time differences up to 500ms. The max time difference we can allow for our application is ~100ms. Now we have already used the Meinberg NTPd for Windows. It works great except we have one big issue with it: If there is a network connection problem between the client and server, the ntp server is in a panic state It won't give the client a new time until we restart the ntp service. This is a big issue which has caused us some trouble. It was working fine for months until there was a network problem we didn't notice, we only noticed it after a week when the time difference was already 30 sec. on the clients. So please suggest some alternative NTP Server for windows. I did Google but I get a lot of unrelated search results. Edit: So far the ntpd windows version was very accurate and I'd like to stick with it. The only problem is the "panic state" after a network disconnect. Maybe some knows here what the cause of this is and how to fix it. Also, I forgot to mention that we have a server/client setup like this: Server1 -- Server2 -- Server3 -- Client1 -- Client2 -- Client3 So Server2 gets its time from Server1, Server3 gets its time from Server2, and the Clients get their time from Server3. Also, there are clients connected directly to Server2. It is important that all Servers and Clients have the exact same time (within ~100ms) Now there was a network problem with Server3 and its clients. The servers run the ntpd port for Windows, which acts as NTP server and client. The clients have Dimension4 as NTP client. After the network problem, the error message in D4 was something like this (out the top of my head, don't have the exact error message): Server response: The server is in a panic state (could not sync clock) I read through the ntpd docs, and the only mention of "panic" is when the time difference is 10000 seconds which will cause to exit the ntpd server but this was not the case. Also there is a "-g" command line switch to disable the panic exit, but it is already set by default. Any ideas what could cause the panic state and how to get rid of it next time?

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• compile ntp without ssl

  - by Zulakis

  I need to deploy ntp to a very space-critical pxe-imaging-system. (Yes, each KB matters.) Footprint needs to be as small as possible, so I want to compile ntp without linking openssl. According to the manual this is should be possible: If available, the OpenSSL library from http://www.openssl.org is used to support public key cryptography. The library must be built and installed prior to building NTP. The procedures for doing that are included in the OpenSSL documentation. The library is found during the normal NTP configure phase and the interface routines compiled automatically. Only the libcrypto.a library file and openssl header files are needed. If the library is not available or disabled, this step is not required. I already tried out ./configure --without-openssl however, this didn't help. This is my ldd output: ldd ntpd/ntpd linux-gate.so.1 => (0xb7706000) libm.so.6 => /lib/i686/cmov/libm.so.6 (0xb76d5000) libcrypto.so.0.9.8 => /usr/lib/i686/cmov/libcrypto.so.0.9.8 (0xb7582000) librt.so.1 => /lib/i686/cmov/librt.so.1 (0xb7578000) libc.so.6 => /lib/i686/cmov/libc.so.6 (0xb741d000) /lib/ld-linux.so.2 (0xb7707000) libdl.so.2 => /lib/i686/cmov/libdl.so.2 (0xb7419000) libz.so.1 => /usr/lib/libz.so.1 (0xb7404000) libpthread.so.0 => /lib/i686/cmov/libpthread.so.0 (0xb73eb000) The system I am compiling on is 32-bit debian lenny using openssl 0.9.8g-15+lenny16. What is the correct configure option to compile ntp without openssl?

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• Will NTP work in an isolated network ( in absence of a reliable time source)

  - by Anand

  Hi, I am investigatiing a typical NTP problem. The setup is as follows :- FreeBSD is being compiled and run on Opensolaris. The config file on OpenSolaris has entry of linux and another opensolaris machine as server and these server machines are syncing time with themselves (local clock) only. The server machines in this case have NTP running on them as well. Within a few minutes of starting the ntp daemon ,client starts syncing time with itself only and remains in that situation after that.All servers are discarded and no time syncing is done with them. My question is , is there any fundamental problem with this setup. Will the NTP work in such isloated network that has no direct or indirect connection with reliable internet time source ?

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• NTP daemon or ntpdate doesn't synchronize

  - by user2862333

  I'm having some problems with synchronization with an NTP server. 1) The NTP daemon doesn't sync the system clock at all, even though it's running (confirmed with /etc/init.d/ntp status). Forcing to sync with ntpd -q or ntpd -gq does not work either. 2) Stopping the NTP daemon and syncing manually with ntpdate does give me the following output: ~# ntpdate -d 0.debian.pool.ntp.org 6 Nov 16:48:53 ntpdate[4417]: ntpdate [email protected] Sat May 12 09:07:19 UTC 2012 (1) transmit(79.132.237.5) receive(79.132.237.5) transmit(85.234.197.2) receive(85.234.197.2) transmit(194.50.97.34) receive(194.50.97.34) transmit(79.132.237.1) receive(79.132.237.1) transmit(79.132.237.5) receive(79.132.237.5) transmit(85.234.197.2) receive(85.234.197.2) transmit(194.50.97.34) receive(194.50.97.34) transmit(79.132.237.1) receive(79.132.237.1) transmit(79.132.237.5) receive(79.132.237.5) transmit(85.234.197.2) receive(85.234.197.2) transmit(194.50.97.34) receive(194.50.97.34) transmit(79.132.237.1) receive(79.132.237.1) transmit(79.132.237.5) receive(79.132.237.5) transmit(85.234.197.2) receive(85.234.197.2) transmit(194.50.97.34) receive(194.50.97.34) transmit(79.132.237.1) receive(79.132.237.1) server 79.132.237.5, port 123 stratum 2, precision -20, leap 00, trust 000 refid [79.132.237.5], delay 0.05141, dispersion 0.00145 transmitted 4, in filter 4 reference time: d624e3b1.f490b90d Wed, Nov 6 2013 16:50:09.955 originate timestamp: d624e457.eaaf787c Wed, Nov 6 2013 16:52:55.916 transmit timestamp: d624e36c.4a7036fd Wed, Nov 6 2013 16:49:00.290 filter delay: 0.08537 0.05141 0.05151 0.06346 0.00000 0.00000 0.00000 0.00000 filter offset: 235.6038 235.6087 235.6095 235.6068 0.000000 0.000000 0.000000 0.000000 delay 0.05141, dispersion 0.00145 offset 235.608782 server 85.234.197.2, port 123 stratum 2, precision -20, leap 00, trust 000 refid [85.234.197.2], delay 0.05151, dispersion 0.00336 transmitted 4, in filter 4 reference time: d624e3e7.dc6cd02b Wed, Nov 6 2013 16:51:03.861 originate timestamp: d624e458.1c91031f Wed, Nov 6 2013 16:52:56.111 transmit timestamp: d624e36c.7da1d882 Wed, Nov 6 2013 16:49:00.490 filter delay: 0.05765 0.07750 0.06013 0.05151 0.00000 0.00000 0.00000 0.00000 filter offset: 235.6048 235.6014 235.6035 235.6078 0.000000 0.000000 0.000000 0.000000 delay 0.05151, dispersion 0.00336 offset 235.607826 server 194.50.97.34, port 123 stratum 3, precision -23, leap 00, trust 000 refid [194.50.97.34], delay 0.03021, dispersion 0.00090 transmitted 4, in filter 4 reference time: d624e38d.2bce952c Wed, Nov 6 2013 16:49:33.171 originate timestamp: d624e458.4dbbc114 Wed, Nov 6 2013 16:52:56.303 transmit timestamp: d624e36c.b0d38834 Wed, Nov 6 2013 16:49:00.690 filter delay: 0.03030 0.03636 0.03091 0.03021 0.00000 0.00000 0.00000 0.00000 filter offset: 235.6095 235.6085 235.6098 235.6105 0.000000 0.000000 0.000000 0.000000 delay 0.03021, dispersion 0.00090 offset 235.610589 server 79.132.237.1, port 123 stratum 3, precision -20, leap 00, trust 000 refid [79.132.237.1], delay 0.05113, dispersion 0.00305 transmitted 4, in filter 4 reference time: d624dfcb.6acea332 Wed, Nov 6 2013 16:33:31.417 originate timestamp: d624e458.838672ad Wed, Nov 6 2013 16:52:56.513 transmit timestamp: d624e36c.e405181c Wed, Nov 6 2013 16:49:00.890 filter delay: 0.06345 0.05113 0.05681 0.05656 0.00000 0.00000 0.00000 0.00000 filter offset: 235.6087 235.6038 235.6010 235.6074 0.000000 0.000000 0.000000 0.000000 delay 0.05113, dispersion 0.00305 offset 235.603888 6 Nov 16:49:00 ntpdate[4417]: step time server 79.132.237.5 offset 235.608782 sec Clearly, ntpdate can reach the NTP server(s), but after checking the clock, it hasn't changed and is still displaying the wrong time. Any ideas what would be the problem would be much appreciated.

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