Overview of time configuration under Linux system

1. Time types are divided into:

1. Network time (set time zone, time synchronized by ntp server)

2. System time, the time displayed by the current system

3. Hardware (RTC) time, Bios time on the motherboard

The general settings are: system time is synchronized with network time, and system time is written into hardware time.

2. How to view the time:

1. Check the hardware time

#hwclock

2. Check the system time

date

3. Update and check network time

#ntpdate xxxxxx
xxxxxx is the time server set in the /etc/ntp.conf file

4. How to modify the time

1. Modification of system time

Set the time to 13:11:03 #date -s 13:11:03

2. Hardware time modification

#hwclock --set --date='03/21/2019 15:20';

Set the hardware time to 15:20 on March 21, 2019

3. Modification of network time

1. The network time needs to be modified by changing the time zone. tzselect If you are not sure about the time zone, you need to use this command to find your time zone. 2. Most Chinese users use Asia/Shanghai, so use the following command to update to Shanghai time zone #cp -v /usr/share/zoneinfo/Asia/Shanghai /etc/localtime
3. Synchronize time with the network server #ntpdate xxxxxx
xxxxxx is the time server set in the /etc/ntp.conf file

5. Time write to each other

1. Hardware time is written to system time

#hwclock -s

2. System time synchronizes network time

#ntpdate xxxxxx
xxxxxx is the time server set in the /etc/ntp.conf file

3. System time is written to hardware time

#hwclock -w

6. Causes and solutions to the dual system time error problem

1. Hardware time format

1. Local time: localtime (the time used by Windows)

2. World Standard Time: UTC (the time used by Linux/Unix)

2. Differences between Windows and Linux/Unix in interpreting hardware time

Windows uses localtime as the system time

Linux/Unix uses the time converted from UTC (Universal Standard Time) and the time zone as the system time. Since Beijing time uses the Eastern Time Zone 8, the system time is converted from UTC+8.

3. Reasons for time discrepancy between Windows and Linux/Unix

When using the Windows system, the localtime is written into the hardware time while synchronizing the time with the network (note that the Windows system time and the hardware time are synchronized to the same time at this time). When using the Linux/Unix setting, the hardware time is UTC time, so it adds 8 hours to the correct time that has been synchronized, and vice versa, resulting in time error.

4.Solution to time discrepancy between Windows and Linux/Unix

Method 1. Windows:

1. Use UTC time as local time

Method 2. Linux:

1. Use localtime as hardware time (suitable for Linux distributions that use systemd to manage services)

2. Use network time as local time and do not synchronize with hardware time (applicable to Linux distributions that use init management services)

Most distributions currently use systemd as the service manager.

5. Specific operations of time difference between Windows and Linux/Unix

Method 1: Windows

1. Open cmd as administrator

implement:

Reg add HKLM\SYSTEM\CurrentControlSet\Control\TimeZoneInformation /v RealTimeIsUniversal /t REG_DWORD /d 1

Method 2: Linux

1. Use localtime as hardware time (suitable for Linux distributions that use systemd to manage services)

#hwclock --localtime

or

The root user modifies the UTC of the file /etc/adjtime file to LOCAL

2. Set Linux not to use hardware time synchronization (applicable to Linux distributions that use init management services)

The root user modifies the content of the file /etc/sysconfig/clock from UTC=1 to UTC=0

If there is anything missing, please comment and supplement!

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