Linux时钟简介 RedHat Linux操作系统修改时区的方法

　　http://www.cnblogs.com/cy163/archive/2008/05/15/1198683.html
　　RedHat Linux操作系统修改时区的方法
　　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>　　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:
　　# cd /etc
　　# ls -al localtime
　　lrwxrwxrwx 1 root root 39 Mar 28 07:00 localtime -> /usr/share/zoneinfo/America/Los_Angeles
　　# rm /etc/localtime
　　# ln -s /usr/share/zoneinfo/America/Denver /etc/localtime
　　# ls -al localtime
　　lrwxrwxrwx 1 root root 34 Mar 28 08:59 localtime -> /usr/share/zoneinfo/America/Denver
　　# date
　　Fri Mar 28 09:00:04 MST 2003
　　######################################################################

[root@pcmk2 ~]# date

　　Fri Oct 17 06:53:24 EDT 2014

[root@pcmk2 ~]# mv /etc/localtime /etc/localtime-old

[root@pcmk2 ~]# ln -s /usr/share/zoneinfo/America/Denver /etc/localtime

[root@pcmk2 ~]# vim /etc/sysconfig/clock

[root@pcmk2 ~]# date

　　Fri Oct 17 05:04:20 MDT 2014