Crontab can be used to create timing tasks under Linux.
Commonly used matching
crontab -e Edit tasks
crontab -l View all tasks [this user]
crontab -r Cancel all tasks [this user]
Task format
× × × × × +Command (specific tasks)
The first 5 parameters represent time, in turn:
Parameters Range
Minutes 0-59
Hours 0-23
Date 1-31
Month 1-12
Week 0-6 (0 represents Sunday)
Special symbols
In order to accurately represent timing, some special symbols are needed to describe the specific task execution time. There are several symbols:
"/" represents every time, how long does it take to go
"*" represents any time
"-" represents a period of time from one moment to another
"," represents discrete time
Case
0 8 1 1 0command
Command is executed at 8:00 on January 1st every year
*/30 * * * *command
Perform command every 30 minutes
0 6-18 * * *command
Command is executed every day from 6:00 to 18:00
30 6,9,12 * * *command
Command is executed every day at 6:30, 9:30, and 12:30
0 6-18/3 * * */user/bin/PHP
/var/www/html/Execute every 3 hours from 6:00 to 18:00 every 3 hours using /user/bin/php /var/www/html/
Notice
The commands set in crontab are all relative paths, so the scripts executed in the command should be set to an absolute path as much as possible. On the other hand, if there is output in the script, it will be output to the current user directory. Therefore, if there is a path in the script, please set it to an absolute path!
Crontab errors will be sent to the user by email. The directory under centos is /var/spool/mail/user. Long-term accumulation may cause the space under /var/ to take up too much space, so it should be cleaned up in time. (dG in vi)
The above is a detailed explanation introduced by the editor to create timed tasks using crontab under Linux. I hope it will be helpful to everyone. If you have any questions, please leave me a message and the editor will reply to everyone in time. Thank you very much for your support for my website!