Background - The Earth is divided into time zones that are 15 degrees of longitude each, for this corresponds to the amount of angular distance the Sun appears to travel in 1 hour. 0 degrees longitude runs through the Royal Observatory in Greenwich, England. This is the origin of Greenwich Mean Time, or GMT. For all practical purposes, GMT and UTC are the same. To complicate matters, some countries observe Daylight Savings Time (DST), while others do not. Even within some countries, some states or districts do not observe DST while the rest of the country does! DST can also begin and end on different days in different countries! What a mess...
There are several files and directories that are used for time zones, and several tools:
l/etc/sysconfig/clock- this is a short text file that defines the timezone, whether or not the hardware clock is using UTC, and an ARC option that is only relevant to DEC systems.
eg：/ect/sysconfig/clock file content on jstest3:
ZONE="Asia/Shanghai"
UTC=true
ARC=false
l/etc/localtime - this is a symbolic link to the appropriate time zone file in /usr/share/zoneinfo
l/usr/share/zoneinfo - this directory contains the time zone files that were compiled by zic(The time zone compiler. Zic creates the time conversion information files.)These are binary files and cannot be viewed with a text viewer. The files contain information such as rules about DST. They allow the kernel to convert UTC UNIX time into appropriate local dates and times.
l/etc/rc.d/rc.sysinit- This script runs once, at boot time. A section of this script sets the system time from the hardware clock and applies the local time zone information.
l/etc/init.d/halt- This script runs during system shutdown. A section of this script synchronizes the hardware clock from the system clock.
l/etc/adjtime - This file is used by the adjtimex function, which can smoothly adjust system time while the system runs. settimeofday is a related function.
lredhat-config-date or dateconfig - These commands start the Red Hat date/time/time zone configuration GUI.
lzdump - This utility prints the current time and date in the specified time zone. Example:
Most modern Linux distributions have user-friendly programs to set the timezone, often accesible through the program menus or right-clicking the clock in a desktop environment such as KDE or GNOME. Failing that it's possible to manually change the system timezone in Linux in a few short steps.
It's possible to change the system timezone in Linux in a few short steps.
Steps
1.Logged in as root, check which timezone your machine is currently using by executing `date`. You'll see something like "Mon 17 Jan 2005 12:15:08 PM PST -0.461203 seconds", PST in this case is the current timezone.
2.Change to the directory to /usr/share/zoneinfo, here you will find a list of time zone regions. Choose the most appropriate region, if you live in Canada or the US this directory is the "Americas" directory.
3.If you wish, backup the previous timezone configuration by copying it to a different location. Such as `mv /etc/localtime /etc/localtime-old`.
4.Create a symbolic link from the appropiate timezone to /etc/localtime. Example: `ln -s /usr/share/zoneinfo/Europe/Amsterdam /etc/localtime`.
5.If you have the utility rdate, update the current system time by executing `/usr/bin/rdate -s time.nist.gov`. (This step can be skip!)
6.Set the ZONE entry in the file /etc/sysconfig/clock file (e.g. "America/Los_Angeles")
7.Set the hardware clock by executing: ` /sbin/hwclock --systohc`
Tips
·On some versions of RedHat Linux, Slackware, Gentoo, SuSE, Debian, Ubuntu, and anything else that is "normal", the command to display and change the time is 'date', not 'clock'
·On RedHat Linux there is a utility called "Setup" that allows one to select the timezone from a list, but you must have installed the 'redhat-config-date' package.
Warnings
·Some applications (such as PHP) have separate timezone settings from the system timezone.
·On some systems, /etc/localtime is actually a symlink to the appropriate file under the /usr/share/zoneinfo directory (rather than a copy of that file).
·On some systems, there is a system utility provided that will prompt for the correct timezone and make the proper changes to the system configuration. For example,Debianprovides the "tzsetup" utility.
Here is an example of changing the timezone: (Logged in as root)
In order to manually change the timezone, you can edit the /etc/sysconfig/clockfile and then make a new soft link to /etc/localtime. Here is an example of changing the timezone manually to "America/Denver":
1. Select the appropriate time zone from the /usr/share/zoneinfo directory. Time zone names are relative to that directory. In this case, we will select "America/Denver"
2. Edit the /etc/sysconfig/clocktext file so that it looks like this:
ZONE="America/Denver"
UTC=true
ARC=false
Of course, this assumes that your hardware clock is running UTC time...
3. Delete the following file: /etc/localtime (backup it when you need it !)
4. Create a new soft link for /etc/localtime. Here is an example of step 3 and step 4:
根据上面的提示，我把 TZ='Asia/Shanghai'; export TZ加到了root用户下的 .bash _profile 最后面，重新logout然后login，再次查询的时候就成功了。。。。方法(2) 仅限于RedHat Linux 和 CentOS timeconfig
