Date command to get the current date.

$ date=$(date +%Y-%m-%d)
$ echo $date

Date command to get yesterday’s date.

$ date=$(date --date=yesterday +%Y-%m-%d)
$ echo $date

Date command to get tomorrow’s date.

$ date=$(date --date=tomorrow +%Y-%m-%d)
$ echo $date

Performing arithmetical operations on date.

Below example will subtract 1 hour from the current date time.

$ strdate=`date --date=now +"%s"`
$ strdate=`expr $strdate - 3600`
$ date=`date -d "1970-01-01 $strdate sec" +"%a %b %d %H:%M"`

OpenNTPD is a Unix system daemon implementing the Network Time Protocol to synchronize the local clock of a computer system with remote NTP servers.

OpenNTPD is primarily developed by Henning Brauer as part of the OpenBSD project. Its design goals include being secure (non-exploitable), easy to configure, accurate enough for most purposes and with source code that can be distributed under a BSD license.

This tool helped me a lot. Using openntpd we can set the same time on multiple system.

Installation

$ sudo apt-get install openntpd

Openntp configuration file /etc/openntpd/ntpd.conf

To set the time use the command ntpdate-debian

$ sudo ntpdate-debian
[sudo] password for shahid:
 7 Aug 00:20:33 ntpdate[26597]: adjust time server 59.165.131.82 offset -0.089443 sec