安装完默认配置：
$timedatectl status
Local time: 一 2017-07-24 15:02:43 UTC
Universal time: 一 2017-07-24 15:02:43 UTC
RTC time: 一 2017-07-24 15:02:50
Time zone: Etc/UTC (UTC, +0000)
Network time on: no
NTP synchronized: no
RTC in local TZ: yes
修改到上海后
timedatectl status
Local time: 一 2017-07-24 23:10:15 CST
Universal time: 一 2017-07-24 15:10:15 UTC
RTC time: 一 2017-07-24 23:10:14
Time zone: Asia/Shanghai (CST, +0800)
Network time on: no
NTP synchronized: no
RTC in local TZ: yes
Warning: The system is configured to read the RTC time in the local time zone.
This mode can not be fully supported. It will create various problems
with time zone changes and daylight saving time adjustments. The RTC
time is never updated, it relies on external facilities to maintain it.
If at all possible, use RTC in UTC by calling
'timedatectl set-local-rtc 0'.
timedatectl set-local-rtc 0
$ timedatectl status
Local time: 一 2017-07-24 23:14:38 CST
Universal time: 一 2017-07-24 15:14:38 UTC
RTC time: 一 2017-07-24 15:14:38
Time zone: Asia/Shanghai (CST, +0800)
Network time on: no
NTP synchronized: no
RTC in local TZ: no
整个地球分为二十四时区，每个时区都有自己的本地时间。在国际无线电通信场合，为了统一起见，使用一个统一的时间，称为通用协调时(UTC, Universal Time Coordinated)。UTC与格林尼治平均时(GMT, Greenwich Mean Time)一样，都与英国伦敦的本地时相同。在本文中，UTC与GMT含义完全相同。
