In Linux all metadata about file are stored in UTC (Coordinated Universal Time) time. Regardless of your location.
So when we run
stat filename. The information that it show is stored in UTC. However when it show us the information then it show it in our local time.
bob@vmUbuntu:/etc$ stat at.deny File: 'at.deny' Size: 144 Blocks: 8 IO Block: 4096 regular file Device: 801h/2049d Inode: 151430 Links: 1 Access: (0640/-rw-r-----) Uid: ( 0/ root) Gid: ( 1/ daemon) Access: 2016-08-19 19:26:01.950906000 +0300 Modify: 2016-01-15 00:35:27.000000000 +0200 Change: 2016-08-19 19:26:01.950906000 +0300 Birth: -
However the date stamp is stored always in UTC, when we see it, then it convert it to our local-time.
It order to do this conversion Linux need to know what it our local timezone. It do this by check the file /etc/localtime . This file is a symbol link to file inside /usr/share/zoneinfo that has the name of the city of our timezone. zoneinfo directory contain directory for every continent in the world and inside it for all the city in that continent that represent timezone.
By changing the symbolic link /etc/localtime and making it to point to anther file (that represent city timezone), we de facto change our timezone.
A quick way to see our current timezone is to use the
bob@vmUbuntu:/etc$ date Fri Aug 26 13:45:26 IDT 2016
So in this case we run
date and it told us that our timezone is set to IDT, which is acronym for Israel Daylight Time.
If we want to set individual timezone, we can use the variable TZ, we point it the filename (with full path) of the timezone that we want.
So for example, if we want to change the timezone of a user to Oral timezone (we will set his TZ variable):
bob@vmUbuntu:/etc$ date Fri Aug 26 13:45:26 IDT 2016 bob@vmUbuntu:/etc$ export TZ=/usr/share/zoneinfo/Asia/Oral bob@vmUbuntu:/etc$ date Fri Aug 26 16:18:15 +05 2016
As we can see that timezone was change from IDT to +05. if we want this change to be permanent, we can put it in the login script of this user.
So this allow us to set different timezone for different user.
If we want to see our local setting, we can run the command local:
bob@vmUbuntu:/etc$ locale LANG=en_US.UTF-8 LANGUAGE= LC_CTYPE="en_US.UTF-8" LC_NUMERIC="en_US.UTF-8" LC_TIME="en_US.UTF-8" LC_COLLATE="en_US.UTF-8" LC_MONETARY="en_US.UTF-8" LC_MESSAGES="en_US.UTF-8" LC_PAPER="en_US.UTF-8" LC_NAME="en_US.UTF-8" LC_ADDRESS="en_US.UTF-8" LC_TELEPHONE="en_US.UTF-8" LC_MEASUREMENT="en_US.UTF-8" LC_IDENTIFICATION="en_US.UTF-8" LC_ALL=
So we can see that in the this computer, the local is English united state and the character encoding is UTF-8.
The local define character encoding and how telephone number, paper size, time etc are displayed.
To see all installed locales
locale -a will show all installed locales in our computer.
We can syncronize our computer with the ntpdate command (you may need to install this).
It is better to give it cluster of server address. you can find list of ntp server cluster here: http://www.pool.ntp.org/en/
bob@vmUbuntu:~$ sudo ntpdate il.pool.ntp.org 26 Aug 14:54:48 ntpdate: adjust time server 22.214.171.124 offset 0.010919 sec
We used ntp server in the Israeli cluster, to synchronize our computer clock.
We can use cron to run ntpdate and regularly synchronize our computer clock. A better option maybe to use ntp (time service) and it will syncronize the computer. This service is may need to be installed.