NTP cron job runs every 5 min instead of hour

OlRoy · 02-27-2008, 06:30 PM

I can't figure this out. I have the following crontab entry

Code:

0 * * * * ntpdate us.pool.ntp.org

It should go once ever hour, but according to tcpdump I see the NTP traffic around once every 5 minutes.

Code:

19:11:33.389970 IP 192.168.1.107.123 > 63.240.161.99.123: NTPv4, Client, length 48
19:11:33.441194 IP 63.240.161.99.123 > 192.168.1.107.123: NTPv4, Server, length 48
19:16:57.349480 IP 192.168.1.107.123 > 63.240.161.99.123: NTPv4, Client, length 48
19:16:57.401427 IP 63.240.161.99.123 > 192.168.1.107.123: NTPv4, Server, length 48
19:21:18.346288 IP 192.168.1.107.123 > 63.240.161.99.123: NTPv4, Client, length 48
19:21:18.397088 IP 63.240.161.99.123 > 192.168.1.107.123: NTPv4, Server, length 48
19:26:41.349543 IP 192.168.1.107.123 > 63.240.161.99.123: NTPv4, Client, length 48
19:26:41.404663 IP 63.240.161.99.123 > 192.168.1.107.123: NTPv4, Server, length 48

I have no clue what's going on... does anyone know how to fix this?

Update: I just deleted the cronjob with crontab -r and it is still syncing every 5 minutes, and I still can't figure it out...

billymayday · 02-27-2008, 06:47 PM

See if there's a daemonised process or similar running (are you running ntpd?)

ps aux | grep ntp

OlRoy · 02-27-2008, 07:11 PM

Yeah only ntpd is running. Is that what's causing this?

Emerson · 02-27-2008, 07:49 PM

Quote:

Originally Posted by OlRoy

Yeah only ntpd is running. Is that what's causing this?

Yep, and this is something you want to keep running. Even computer security relies on correct time.

OlRoy · 02-28-2008, 06:06 AM

Well I tried disabling NTPD and only using a cron ntpdate job, but no NTP traffic was sent. Which is odd since I can use ntpdate manually and NTP traffic is sent so I don't know why cron isn't working.

scowles · 02-28-2008, 06:42 AM

Try adding a "user" to cron job entry. Example:

0 * * * * root ntpdate us.pool.ntp.org

Emerson · 02-28-2008, 07:05 AM

ntpd does more than you think, it keeps correct time even between syncing using drift file. I do not understand why someone would want to disable it.

OlRoy · 02-28-2008, 07:17 AM

Quote:

Originally Posted by scowles

Try adding a "user" to cron job entry. Example:

0 * * * * root ntpdate us.pool.ntp.org

I have the following crontab entry now and it still isn't working.

2 * * * * * root ntpdate us.pool.ntp.org
1 * * * * * root echo Testing

I checked and the crond is running as well. This is all on a Red Hat 9 box if it matters...

OlRoy · 02-28-2008, 07:20 AM

Quote:

Originally Posted by Emerson

ntpd does more than you think, it keeps correct time even between syncing using drift file. I do not understand why someone would want to disable it.

I'm just trying to get it working and disabled it for trouble shooting. How can I get ntpd to sync once every 30 or maybe 60 minutes instead of every 5 minutes? If I can't figure out why cron isn't working I'll use ntpd, but I'd really like to get cron working just so I know what in the heck is going on.

bathory · 02-28-2008, 07:33 AM

Use the full path to ntpdate command and the "-s" option:

Code:

0 * * * * /usr/sbin/ntpdate -s us.pool.ntp.org

OlRoy · 02-28-2008, 07:47 AM

Man with your suggestion and what I just found on a website I thought I had it. The website said use */n * * * * command to run something every n minutes. My current crontab looks like this

Code:

1 * * * * /usr/sbin/ntpdate -s us.pool.ntp.org
*/2 * * * * /usr/sbin/ntpdate -s us.pool.ntp.org

After a few minutes of waiting I still don't see any NTP traffic.

Emerson · 02-28-2008, 07:51 AM

Yes, but if your computer clock is not accurate enough then running ntpdate will cause time jumps. Depending how big those jumps are you may get weird errors.

OlRoy · 02-28-2008, 07:57 AM

Emerson, then how can I tell ntpd how often I want it to sync to the NTP server? I haven't found anything in the /etc/ntp.conf or google on how to do that.

OlRoy · 02-28-2008, 08:20 AM

It works! I just checked my mail and cron was complaining that the root command wasn't found so I deleted root and cron finally works now. Thanks for everyones help!

Emerson I'm still interested in using ntpd if it's possible to change how often it syncs with the ntp server.

Emerson · 02-28-2008, 08:24 AM

Is it new install? Once ntpd gets "familiar" with your computer clock it should increase the sync interval to 1024 s, isn't this interval long enough?