The NTP socket is in use, exiting, Linux

Ntpdate [21718]: Output, NTP socket is in use

# ntpdate
28 Feb 02:04:45 ntpdate[15432]: the NTP socket is in use, exiting

This can happen because the ntp service is running. Depends on your Linux version if you want to stop the NTP service and restart Ntpdate. Before starting the NTP service again.

$ sudo service ntp stop
Stopping NTP server: ntpd.
$ sudo ntpdate
28 Feb 02:06:14 ntpdate[15593]: adjust time server offset -0.220254 sec 
$ sudo service ntp start
Starting NTP server: ntpd.

Or use the following command, which will use a different port:

# ntpdate -u