Detailed explanation of the installation and use of Linux scheduled tasks crontabs

Install crontab

yum install crontabs

CentOS 7 comes with it, I didn't install it manually

Start/Stop

service crond start // Start the service service crond stop // Shut down the service service crond restart // Restart the service service crond reload // Reload the configuration

Check whether the crontab service is set to start at boot

systemctl list-unit-files | grep enable | grep crond

Add crontab to start automatically at boot

chkconfig crond on
// or systemctl enable crond.service

View crontab status

service crond status // View crontab service status

Writing scheduled task command format

min hour day month dayofweek command
 Time-sharing day, month, and day of week command

​ min: the minute of each hour at which the task is executed; the value range is 0-59

​ hour: the hour of the day to execute the task; the value range is 0-23

​ day: the day of the month to execute the task; the value range is 1-31

​ month: the month of the year when the task is executed; the value range is 1-12

​ dayofweek: the day of the week to execute the task; the value range is 0-6, 0 means weekend

​ command: specifies the command to be executed

There are two ways to edit the command: Enter in the command line: crontab -e and then add the corresponding task, wq save and exit directly edit the /etc/crontab file, that is, vi /etc/crontab , add the corresponding task time format

​ *: indicates any time; for example, * in the hour position indicates every hour

​ n: indicates a specific time; for example, the hour digit 5 ​​means 5 o'clock

​ n,m: Indicates several specific times; for example, the hour digits 1,10 represent 1 o'clock and 10 o'clock

​ n－m: represents a time period; for example, the hour digits 1-5 represent 1 to 5 o'clock.

/n: Indicates how many time units are used to execute the command; for example, hour position /1 means that the command is executed every 1 hour, which can also be written as 1-23/1

Little Chestnut

* 1 * * * ~/clear_cache.sh: Execute the script every 1 minute from 1:00 to 1:590 * * * * ~/clear_cache.sh: Execute the script at 0 minute of every hour*/10 * * * * ~/clear_cache.sh: Execute the script every 10 minutes

Script to clean up system cache

Code:

vim ~/clear_cache_logs.txt
sudo sysctl -w vm.drop_caches=3
sudo sysctl -w vm.drop_caches=1
echo `date -R` >> ~/clear_cache_logs.txt
free -lh >> ~/clear_cache_logs.txt

Clean the memory cache and enter the cleaning time and remaining memory log into the ~/clear_cache_logs.txt file for easy viewing. You can combine it with crontab to do a scheduled task to clean the memory cache regularly.

Summarize

The above is a detailed introduction to the installation and use of Linux crontabs scheduled tasks. I hope it will be helpful to everyone. If you have any questions, please leave me a message and I will reply to you in time. I would also like to thank everyone for their support of the 123WORDPRESS.COM website!
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