修改CentOS服务器时间为北京时间

1. 购买了VPS，CentOS系统，发现服务器时间与北京时间往往不一致，存在时差。

[clive@server workspace]$ date
2018年 05月 30日 星期三 02:02:47 UTC

2. 可以执行tzselect命令按提示更换时区，依次选择5-Asia，9-China，1-Beijing Time。

Please identify a location so that time zone rules can be set correctly.
Please select a continent or ocean.
 1) Africa
 2) Americas
 3) Antarctica
 4) Arctic Ocean
 5) Asia
 6) Atlantic Ocean
 7) Australia
 8) Europe
 9) Indian Ocean
10) Pacific Ocean
11) none - I want to specify the time zone using the Posix TZ format.
#? 5
Please select a country.
 1) Afghanistan		  18) Israel		    35) Palestine
 2) Armenia		  19) Japan		    36) Philippines
 3) Azerbaijan		  20) Jordan		    37) Qatar
 4) Bahrain		  21) Kazakhstan	    38) Russia
 5) Bangladesh		  22) Korea (North)	    39) Saudi Arabia
 6) Bhutan		  23) Korea (South)	    40) Singapore
 7) Brunei		  24) Kuwait		    41) Sri Lanka
 8) Cambodia		  25) Kyrgyzstan	    42) Syria
 9) China		  26) Laos		    43) Taiwan
10) Cyprus		  27) Lebanon		    44) Tajikistan
11) East Timor		  28) Macau		    45) Thailand
12) Georgia		  29) Malaysia		    46) Turkmenistan
13) Hong Kong		  30) Mongolia		    47) United Arab Emirates
14) India		  31) Myanmar (Burma)	    48) Uzbekistan
15) Indonesia		  32) Nepal		    49) Vietnam
16) Iran		  33) Oman		    50) Yemen
17) Iraq		  34) Pakistan
#? 9
Please select one of the following time zone regions.
1) Beijing Time
2) Xinjiang Time
#? 1

The following information has been given:

	China
	Beijing Time

Therefore TZ='Asia/Shanghai' will be used.
Local time is now:	Wed May 30 10:04:16 CST 2018.
Universal Time is now:	Wed May 30 02:04:16 UTC 2018.
Is the above information OK?
1) Yes
2) No
#? 1

You can make this change permanent for yourself by appending the line
	TZ='Asia/Shanghai'; export TZ
to the file '.profile' in your home directory; then log out and log in again.

Here is that TZ value again, this time on standard output so that you
can use the /usr/bin/tzselect command in shell scripts:
Asia/Shanghai

3. 将TZ='Asia/Shanghai'; export TZ这行添加到/etc/profile（所有用户生效）或者~/.bash_profile（当前用户生效）
4. 退出重新登录即可，也可执行source /etc/profile或source ~/.bash_profile立即生效
5. 这时候再执行date查看日期就可以发现时区改为北京时间啦。

[clive@server workspace]$ date
2018年 05月 30日 星期三 10:07:11 CST