How to automatically sync your server time clock with rdate in CentOS 5.5

The linux command "rdate" is very useful to quickly sync your server time clock with an NTP (Network Time Protocol) Server.

There are a few options: rdate [-p] [-s] [-u] [-l] [-t sec] [host...]

-p : Print the time returned by the remote machine.

-s : Set the system time to the returned time.

-u : Use UDP instead of TCP as the transport.

-l : Use syslog to output errors (cron.warning) and output (

-t : Set timeout in seconds for every attempt to retrieve date.


Step 1: Make sure you have rdate and cron installed

yum install rdate vixie-cron


Step 2: Pick a server to use to sync time with.

List of HOSTNAME's:


Step 3: Edit your cron and add a schedule to run the command as often as needed within reason.

(Generally once a day is acceptable)

Add the following to your cron: replace the HOSTNAME with one from the list above

0 6 * * * /usr/bin/rdate -s HOSTNAME 2>&1 >> /dev/null

NOTE: 0 6 * * * means: Check once at 6:00 AM every day

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