Yesterday, the power of Ubuntu motherboard was turned off, resulting in a clock error when compiling after restart:
make: Warning: File 'main.cpp' has modification time 8221891 s in the future g++ -MD -MP -MT "./Bin/Intermediate/Arm64-Release/3D/main.d Bin/Intermediate/Arm64-Release/3D/main.o" -c -I/usr/local/include/opencv -I/usr/local/include -O2 -DNDEBUG -I../../include -I/home/work/OpenNI-Linux-Arm64-188.8.131.52/include -DXN_NEON -fPIC -fvisibility=hidden -Werror -o Bin/Intermediate/Arm64-Release/3D/main.o main.cpp cp -R /home/work/OpenNI-Linux-Arm64-184.108.40.206/Redist/* Bin/Arm64-Release g++ -o Bin/Arm64-Release/3D ./Bin/Intermediate/Arm64-Release/3D/main.o -L/usr/local/lib -lopencv_dnn -lopencv_ml -lopencv_objdetect -lopencv_shape -lopencv_stitching -lopencv_superres -lopencv_videostab -lopencv_calib3d -lopencv_features2d -lopencv_highgui -lopencv_videoio -lopencv_imgcodecs -lopencv_video -lopencv_photo -lopencv_imgproc -lopencv_flann -lopencv_core -LBin/Arm64-Release -lOpenNI2 -Wl,-rpath ./ make: Warning: clock error detected. Your creation may be incomplete.
At that time, the time in the system became 2020, but the time zone difference between UTC and CST was correct, that is, the difference was 8 hours.
Local time is now: Fri Nov 20 23:41:25 CST 2020. Universal Time is now: Fri Nov 20 15:41:25 UTC 2020.
2 clock related knowledge
Linux clock is divided into system clock and hardware clock. The system clock refers to the clock in the current Linux Kernel. The hardware clock is the clock powered by battery on the motherboard. This hardware clock can be set in BIOS. When Linux starts, the hardware clock will read the settings of the system clock, and then the system clock will operate independently of the hardware.
All commands (including functions) in Linux are set by the system clock. In Linux, the commands for clock viewing and setting mainly include date, clock and hwlock. The usage of clock and hwlock is similar, and only one is needed, but the clock command supports not only x86 hardware system, but also Alpha hardware system.
3 modification time
3.1 setting the time zone
My own time zone setting is OK. This is just for demonstration.
3.1.1 viewing time zone
Local time: Wed 2021-02-24 11:05:12 CST Universal time: Wed 2021-02-24 03:05:12 UTC RTC time: Wed 2021-02-24 03:05:11 Time zone: Asia/Shanghai (CST, +0800) Network time on: yes NTP synchronized: no RTC in local TZ: no
date -R Wed, 24 Feb 2021 14:21:30 +0800
3.1.2 setting the time zone
Using the tzselect command
Pop up selector
Please identify a location so that time zone rules can be set correctly. Please select a continent, ocean, "coord", or "TZ". 1) Africa 2) Americas 3) Antarctica 4) Asia 5) Atlantic Ocean 6) Australia 7) Europe 8) Indian Ocean 9) Pacific Ocean 10) coord - I want to use geographical coordinates. 11) TZ - I want to specify the time zone using the Posix TZ format. #?
Enter 4 and press enter to prompt:
Please select a country whose clocks agree with yours. 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 #?
Similarly, Enter 9 and press Enter to prompt:
Please select one of the following time zone regions. 1) Beijing Time 2) Xinjiang Time #?
Press 1 to prompt:
The following information has been given: China Beijing Time Therefore TZ='Asia/Shanghai' will be used. Local time is now: Wed Feb 24 11:42:59 CST 2021. Universal Time is now: Wed Feb 24 03:42:59 UTC 2021. Is the above information OK? 1) Yes 2) No #?
Enter 1 and press enter to prompt:
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
Tips here can be found in the home directory In the profile file, manually add TZ, the environment variable is' Asia/Shanghai ', and then log out and login will take effect.
In fact, the above interactive operation executes the script / usr/bin/tzselect.
3.1.3 set time zone file
Execute the command to link the time zone file with the local time setting.
sudo ln -sf /usr/share/zoneinfo/Asia/Shanghai /etc/localtime
3.2. Modify system time
Use the ntpdate tool to synchronize network time.
3.1.1 install ntpdate
sudo apt-get install ntpdate
3.1.2 execute command
Synchronize the time. Pay attention to the address of ntp organization in China
sudo ntpdate cn.pool.ntp.org
24 Feb 11:37:03 ntpdate: step time server 172.18.1.1 offset 8250774.353808 sec
It can be seen that the difference between the local time and the ntp server time is 8250774 seconds, nearly 95.5 days. This is also in line with local time.
View the system time at this time
date Wed Feb 24 11:37:15 CST 2021
3.1.3 synchronize system time to hardware
sudo hwclock --systohc // systohc means to synchronize the system time to the hardware. If hctosys means to synchronize the hardware time to the system time
View the hardware time at this time
sudo hwclock Wed Feb 24 11:38:21 2021 .201714 seconds