What are GMT, UTC and PDT? How to adjust time zone under Linux


GMT is the abbreviation of Greenwich mean time, which can be translated into “Greenwich mean time” or “Greenwich mean time” in Chinese, or “Greenwich mean time” or “Greenwich mean time” in literal translation. Greenwich here is located on the Thames River southeast of London, UK. There is also a Greenwich town in the United States, but it has nothing to do with time


UTC is the abbreviation of coordinated universal time, which is translated into “world standard time” in Chinese. In literal translation, it can be translated into “coordinated universal time” or “coordinated world time”. At present, it means GMT time. Why does it mean GMT?This is because the prime meridian (the meridian is the longitude, the prime meridian is the 0 degree longitude) actually passes through Mecca in the west of Saudi Arabia, not Greenwich in the UK. At that time, the Royal Society of England temporarily determined Greenwich as the crossing point of the original meridian. In addition, Britain was in the period of prosperity, so the whole world used it to the present. Maybe it’s not impossible to change the day to Mecca time as the standard time. So we usually use UTC instead of GMT


PDT is the abbreviation of Pacific Daylight Time, translated into Chinese as “Pacific Daylight Time”, 7 hours later than UTC. Google once mentioned in its Adsense that “on 09-6-13, our engineers will maintain the website from about 10:00 a.m. to 2:00 p.m. on PDT.”

In fact, in addition to PDT time, there is a lot of time in North America:
summer in the United States begins on the first Sunday in April and ends on the last Sunday in October. Daylight saving time is one hour earlier than the normal time , and the corresponding PDT time is PST, pacific standard time. PST after daylight saving time

NST – Newfoundland standard time Newfoundland standard time

NDT – Newfoundland daylight time Newfoundland daylight time

ast – Atlantic Standard Time

ADT – Atlantic daylight time

EST – Eastern Standard Time

EDT – Eastern daylight time

CST – Central Standard Time

CDT – Central daylight time

MST – Mountain Standard Time

MDT – Mountain daylight time

PST – Pacific Standard Time

PDT – Pacific Daylight Time

Akst – Alaska standard time

akdt – Alaska daylight time

had – Hawaii Aleutian standard time Hawaii Aleutian standard time

hadt – Hawaii Aleutian daylight time Hawaii Aleutian daylight time

PST is the Pacific Standard Time (Western eight districts), and the difference between PST and Beijing time (Eastern eight districts) is – 16 hours, that is, Beijing time minus 16 is PST time. PDT is one hour earlier than PST, which means the difference between PDT and Beijing time is – 15 hours

CST (central standard time); It is Chinese standard time
GMT + 8 = UTC + 8 = CST

daylight saving time

Daylight saving time or daylight time

The United States and Canada originally implemented winter time at 2 a.m. on the last Sunday of October every year; Summer time will resume at 2 a.m. on the first Sunday of April

Command timeconfig of changing time zone in Linux system



2010 U.S. daylight time: U.S. 2010 daylight time will start at 02:00 a.m. local time on March 14

At that time, the time server will automatically jump from 01:59:59 to 03:00:00

Beijing time


Solve the problem of the wrong time

Synchronize with the Greenwich mean time server and write as follows:
hardware[ root@ftptest2 ~]#Ntpdate time-a.nist.gov
22 may 13:53:29 ntpdate [27810]: step time server offset – 0.806279 sec
view time:
time[ root@ftptest2 ~]#Date
Tuesday, may 22, 2012 13:53:41 CST

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