Time zone resolution and how to adjust the time zone in Linux

Foreword
Today, I found that the system time of Centos 6.0-64bit in VMware differs from the time of the host machine by several hours. After adjusting the system time, the system restarted and resumed. So I wanted to figure out what the reason was. What is the time zone? Although this basic common sense was mentioned in the geography class of junior high school, traveling abroad is a time-lag. I haven't traveled to China, let alone propose a country. At that time, I really didn't pay much attention to its function. Now that I have used it in my work, I will make up for it.

A few keywords
World time

Universal time is the earliest time standard. In 1884, 1s was internationally determined to be 1 / 8.64 × 104 of the average daily length throughout the year. The time system formed by this standard is called the universal time, that is, UT1. The international atomic time scale was used internationally in 1972. Since then, the time passing the prime meridian of the Old Greenwich Observatory has been called universal time, that is, UT2, or Greenwich Mean Time (GMT), is the universal time corrected for periodic differences in the Earth's rotational speed.

Atomic time

In 1967, people took advantage of the extremely regular characteristics of the cesium atom's oscillation period to develop a high-precision atomic clock. The time it took for the cesium atomic level transition to radiate 9192631770 weeks was set to 1 s. The current atomic time is the international atomic time defined in October 1971. It is the uniform atomic time derived from the comparison of about 200 atomic clocks in the world, and then processed by the International Bureau of Weights and Measures, referred to as TAI.

Coordinated Universal Time

Coordinated Universal Time is a time standard based on the rotation of the earth. Because the earth's rotation speed is not uniform, not every day is exactly 86,400 atomic s, which results in an error of 1 s between 18 months and universal time. In order to correct this kind of error, the International Earth Rotation Research Institute adjusts the Greenwich Mean Time according to the actual situation of the Earth's rotation, and releases the standard time to the world in conjunction with the International Bureau of Weights and Measures. This is the so-called world coordination Hour (UTC: Coordinatde Universal Time). UTC is expressed as: year (y), month (m), day (d), hour (h), minute (min), and second (s), all of which are represented by numbers.

GMT

GMT is the abbreviation of Greenwich Mean Time. It is translated into Chinese as "Greenwich Mean Time" or "Greenwich Mean Time". If translated directly, it can be translated as "Greenwich Mean Time" or "Greenwich Mean Time". Greenwich is here on the Thames, southeast of London, England. In general, its emergence is to regulate the time in all regions of the world. Countries use a fixed time as a reference point to calculate local time. To this end, the International Warp Conference was held in Washington, D.C., in 1884, and Greenwich was determined to be the place where the longitude and the west were zero. People divide the earth artificially into 24 equal parts, each equals a time zone, each time zone spans 15 degrees of longitude, that is, exactly 1 hour in time, and the time zone where Greenwich is located is the middle time zone. We now assume GMT The time is early in the morning of January 10 (0 o'clock), one hour to the west, subtract one hour, the local time is 23 o'clock on the night of January 9, and one hour to the east, plus one hour, then The local time is 1 a.m. on January 10, and so on, and so on. At 120 degrees east longitude, China can be calculated by dividing the degree obtained by (120 ° East-0 ° East Longitude) by 15 to get 8, so China is in East 8 District, then, at this time China is 8 o'clock in the morning on January 10.

UTC

UTC is the abbreviation of Coordinated Universal Time, which is translated into Chinese as "universal standard time". If translated directly, it can be translated as "coordinated universal time" or "coordinated universal time". This is currently referred to as GMT time. Why is it referring to GMT time now? Because the prime meridian (the meridian is the meridian and the prime meridian is the 0 degree meridian) actually passes through Mecca, west of Saudi Arabia, not Greenwich, England. At that time, the Royal Society temporarily determined that Greenwich was the crossing point of the prime meridian. In addition, the United Kingdom was in a period of prosperity and development. It may not be impossible to change the standard time to Mecca. So we generally use UTC instead of GMT.

PDT

PDT is the abbreviation of Pacific Daylight Time, translated into Chinese as "Pacific Daylight Time", which is 7 hours behind UTC time. Google has mentioned in its AdSense that "Our engineers will maintain the site at approximately 10:00 am to 2:00 pm in the PDT at 09-6-13."

PST

The US summer begins on the first Sunday in April and ends on the last Sunday in October. Daylight saving time is one hour earlier than normal time, and the corresponding PDT time is PST, Pacific Standard Time. After the daylight saving time is over, it is PST. PST is Pacific Standard Time (west eight districts), and the time difference between Beijing time (east eight districts) is -16 hours, which is Beijing time minus 16 is PST time. And PDT is one hour earlier than PST, which means that the time difference between PDT and Beijing time is -15 hours

In fact, in addition to PDT and PST time, there is still a lot of time in North America:

Abbreviation Full name Chinese description
NST Newfoundland Standard Time
NDT 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
HAST Hawaii-Aleutian Standard Time
HADT Hawaii-Aleutian Daylight Time

Time zone adjustment under Linux
View the current time zone

[root @ bogon ~] # date -R
Tue, 09 Apr 2013 20:04:40 +0800
Copy the corresponding time zone file and replace the system time zone file; or create a link file

Format: cp / usr / share / zoneinfo / $ primary time zone / $ secondary time zone / etc / localtime
Method 1: cp / usr / share / zoneinfo / Asia / Shanghai / etc / localtime
Method 2: ln -sf / usr / share / zoneinfo / Asia / Shanghai / etc / localtime
Ps: I use the second method to adjust the time in centos.

Reference website:

http://jiangbianwanghai.com/linux/2013/04/09/linux-timezone/