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Auto NTP Time Synchronization

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Operating Systems Linux Red Hat Auto NTP Time Synchronization
# 1  
Question Auto NTP Time Synchronization

Good morning,

My first post and first visit, so hello. I have been asked to see if one of our Linux boxes can have it's time sync automatically because the person who built the system has told our staff it cannot be done. To me that raised some flags because although I am no Linux expert, I just thought, that's impossible.

So I did a bit of research before seeking help form the experts before I try anything.

First thing I came across was the command,

ntpdate <- which would sync the box to public NTP servers

Then this command
crontab -e 
0 4 * * * /usr/sbin/ntpdate <- which would create a schedule to sync every night at 4am

Am I on the right track? We are using Red Hat 5.2 (tikanga), and I don't want to screw anything up, like I said I'm familiar with Linux to some point but no expert. Boils down to wanting this system to synchronize daily with EST Time server.

Thank you for any suggestions and tips or tricks for a linux newb.Smilie

Moderator's Comments:
Mod Comment Please use code tags!

Last edited by YSupport; 12-13-2011 at 02:52 PM.. Reason: code tags, see PM
# 2  
That's almost exactly what we have, except instead of syncing every night at 4am, we do so every boot.

Generally there's no such thing as an 'EST time server'. Your system clock is supposed to be set to time zone 0, Greenwich mean time, and the local time zone controlled by the TZ variable, or a profile file, or other means. If your admin set the clock itself to local time, I'm not sure what to do.

---------- Post updated at 09:17 AM ---------- Previous update was at 09:10 AM ----------

Actually I do know what to do. Run ntpdate -q and see if it wants to advance the time 9 hours or something crazy, or whether it's just off by minutes or seconds. -q tells it not to set the time, just query.
This User Gave Thanks to Corona688 For This Post:
# 3  
Firstly, my apologies for not enclosing my code samples within the proper tags, corrected now.

Thank you Corona688 for the reply. I will do as you mentioned, our system rarely reboots so having our at boot time would not work in my case anyway. Thank you for the explanation of time zone offsets, I never knew this with Linux. Appreciate your input.
# 4  
That seems like such a convoluted way to use NTP, which actually DOES sync time automatically.

Normally, you would just run ntpd and synchronize to a time server, rather than slamming the clock and creating additional drift.
# 5  
Originally Posted by mark54g
That seems like such a convoluted way to use NTP, which actually DOES sync time automatically.

Normally, you would just run ntpd and synchronize to a time server, rather than slamming the clock and creating additional drift.
So mark54g how would your suggestion of running ntpd be utilized on our system then to automatically keep the system continually synchronized because right now they are having to on monthly basis resync cause it drifts 3-4 minutes out. Using the same kind of crontab command to set up the scheduling? Thanks.
# 6  
Absolutely not using cron. ntpd is a daemon. It is constantly running and should be set up via an appropriate ntp.conf file to ensure that it stays within milliseconds, not minutes. You may need a step tickers and drift file, as well as statistics, but you can, with a good time source, be within about 20 milliseconds over the internet without much issue.

Personally, I would suggest you get a master clock, but if you don't need sync to be that tight, you can sync to the internet as long as there are not a lot of machines.

Quick HOWTO : Ch24 : The NTP Server - Linux Home Networking

You should not have to download it, but configure it as instructed.

Essentially, you will end up, with the appropriate configuration and init scripts, set up your server to slew the clock toward the appropriate time so that you are within a margin of error. The speed/latency to the internet does not actually matter as much as the differential between answers, and you should be polling those upstream lower stratum servers every few minutes to make sure you are not out of the ballpark. Then, the algorithm for ntp will be able to "Train" your clock on the server to stay within acceptable ranges by use of a drift file.
This User Gave Thanks to mark54g For This Post:
# 7  
Thank you mark54g, I have set up ntpd and hopefully that should take care of our problem. The service was not running and when I looked it up it was only checking locally, so added a known NTP that were using for our manual execution.

Appreciate you pointing me in the right direction.

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