Task scheduling under Linux includes system task scheduling and user task scheduling. The configuration file for system task scheduling is /etc/crontab. The crontab files for user task scheduling are stored in the /var/spool/cron directory.
We can use the crontab command to create our timed tasks (that is, user task scheduling). For example, we append the current system time to the /home/likeke/demo.txt file every 1 minute :
1. Using the crontab -e command, the following file content appears (detailed usage instructions):
2. Next, enter the following commands under this prompt (five asterisks represent five time parameters, and these time parameters will be explained in detail later):
* * * * * date -d now >> /home/likeke/demo.txt
3. Press ctrl+x to exit, it will prompt whether to save, enter Y to save, and then prompt to save the file name, change it yourself or press Enter to use the default name
4. Restart the cron service:
/etc/init.d/cron restart
5. Complete, open /home/likeke/demo.txt, the effect is as follows:
Time parameter description:
m h dom mon dow
m: Indicates minutes, can be any integer from 0 to 59. h: Indicates the hour and can be any integer from 0 to 23. dom: Represents a date, which can be any integer from 1 to 31. mon: Indicates the month, which can be any integer from 1 to 12. dow: Indicates the day of the week, which can be any integer from 0 to 7, where 0 or 7 represents Sunday.
Time parameter usage example:
1: Execute command every 1 minute Order: * * * * * command 2: Execute once every hour at the 20th minute Order: 20 * * * * command 3: Execute once a day at the 20th minute from 6 am to 8 am Order: 20 6-8 * * * command 4: Execute once a day at the 20th and 40th minutes from 6:00 to 8:00 in the morning Order: 20,40 6-8 * * * command 5: Execute once every Monday at the 20th minute from 6:00 am to 8:00 am Order: 20 6-8 * * 1 command