[ntp:questions] NTP Newbie, can anyone help out ?

Danny Mayer mayer at ntp.isc.org
Sun Dec 3 19:53:26 UTC 2006

apexi.200sx at hotmail.co.uk wrote:
> Hi All,
> I am currently at a site where we have workstations running an
> application program that requires accurate time.  The application
> writes a date time stamp to a database, the dts is generated locally on
> the machine.  Another applcation periodically copies data from the
> original database, to another database querying by the dts since it
> last ran.  This is why the time needs to be accurate on all clients,
> please note though, that the dts resolution is only down to the second.

You can modified your stored procedures so that the database provides
the timestamp rather than the workstations.

> All the client workstations currently use xntpd for time keeping, and
> we have a time server etc. all already configured, thing is we seem to
> still be getting issues where clients aren't having their time adjusted
> correctly, or maybe quickly enough ?

You need to figure out why not. How do you know that that is what is
happening? Are there any firewalls? If you are running Linux, newer
versions of the O/S by the vendors turn on firewalls by default.

> I think NTP is just overkill for this site,

On the contrary, based on your description above, if you want the
workstations to provide the timestamp you *NEED* NTP. Nothing else would
provide you with the accuracy you need.

 I haven't done a full
> in-depth investigation into the NTP RFC's but it seems it is a very
> sophisticated time keeping protocol, and it has an algorithm that
> doesn't just slam the time back in line upon finding clock drift, also
> I have read that there maybe a maximum drift for which the protocol
> will adjust.

You shouldn't worry about the algorithms, they've been developed over
years of experimentation and practice. The drift is something you should
only need to deal with upon startup.

> We have hundreds of workstations and sometimes they may have been
> switched off for a peroid of time, or the CMOS battery may have died -
> does this affect NTP on the whole ?

No, just used the ntpd -g option in the startup and it will reset the
time to the correct time. The -g option allows it to make large
corrections the first time after which ntpd corrects the clock more finely.

> Basically, could someone give me a brief primer on NTP from a
> protocol/algorithm/operational point of view (if possible)

If you really want to see the technical documentation on the algorithms
and implementation you should go to the ntp.org web site here:

> I think we could be better with just a very basic SNTP ?, or just
> UDP/TIME implementation

No, not based on your requirements.

> All we need is for the machine's time to be brought in line
> peroidically accurate to the second from a reference machine.

NTP does much more than this, but it has almost no effect on the running
system so why worry about installing it.

> Unfortunately we can't do this simply with login scripts because a) we
> don't have desktop permissions to change time, and b) users could be
> left logged in for days at a time, so we still need some sort of active
> time management.

NTP requires the privilege to change the time as would any method you
would use to change the time.


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