NTP linux

0 2 * * * /usr/sbin/ntpdate -s -b -p 8 -u 129.132.2.21

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-b

Force the time to be stepped using the settimeofday() system call, rather than slewed (default) using the adjtime() system call. This option should be used when called from a startup file at boot time.

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-p samples

Specify the number of samples to be acquired from each server as the integer samples, with values from 1 to 8 inclusive. The default is 4.



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-s



Divert logging output from the standard output (default) to the system syslog facility. This is designed primarily for convenience of cron scripts.



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-u

Direct ntpdate to use an unprivileged port or outgoing packets. This is most useful when behind a firewall that blocks incoming traffic to privileged ports, and you want to synchronise with hosts beyond the firewall. Note that the -d option always uses unprivileged ports.