[ntp:questions] NTP daemon - fixed offset against real time

msmucr at gmail.com msmucr at gmail.com
Sun Jan 27 22:05:59 UTC 2008

On 26 Led, 23:16, Unruh <unruh-s... at physics.ubc.ca> wrote:
> David Woolley <da... at ex.djwhome.demon.co.uk.invalid> writes:
> >msm... at gmail.com wrote:
> >> i would like to ask you for help or ideas with one ntp related task.
> >> I need to setup one ntp server to serve its sntp clients
> >> with time, which is specific amount of time (several seconds) in
> >You would need to modify the source code to do that.  If you do so,
> >please also overwrite the stratum, reported to clients, with 15, so that
> >if anyone else does try to use you as a server, they won't be able to
> >further distribute broken time.  (It may also be possible to set a silly
> >root dispersion, if the SNTP clients are not too fussy about it, to
> >completely stop NTP clients using the server adding your time offset to
> >root dispersion would be reasonably honest, as long as it is more then
> >one second.)
> I would think it would be both easier and much less prone to introducing
> bugs if theprogram running TV stuff added on the offset. Come two years
> from now you will forget that the time on the machines is munged time, and
> use it as real time.
> \on \Linux you could probably define a special timezone which was x seconds
> off UTC.
> The refclocks off course have the offset option on some of them-- I do not
> think it limits you as to how big that could be-- ie get a GPS source, use
> the NMEA as a clock, and put in the appropriate offset.
> >> advance against correct real time taken from another ntp server in
> >> network. I did some search in documentation from both ntpd and
> >> openntpd, but i didn't find any configuraition option related to this.
> >One wouldn't expect the facility to deliberately break them in this way.
> >> I need this quirky thing due to time syncing of several broadcast
> >> graphics servers which also generates clocks to TV picture and it is
> >> necessary to compensate delay caused by MPEG coding and transmission
> >> of TV signal.

Situation changed a little bit, because there is possibility to use
standalone GPS synced video timecode generator with NTP server card,
which has possibility of setting fixed offset in msec. So this is
probably best solution mentioned by Mr. Unruh.

I tried also fudge directive in ntp.conf, but it works only with local
hw clocks as my server isn't equiped with any GPS or some radio
Tips with compiling of custom timezone file with zic for clients or
writing patch to ntp daemon are also interesting solutions and
although i won't use for this project, it guided me to explore another
unix tools and reading ntp daemon sources.. So thanks to all for their

Kind regards

Michal Smucr

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