Linux Scheduled Tasks Crontab notes and summaries (2) Basic composition and configuration of Crontab

"The basic composition of Crontab"

① system service CROND: Refreshes the scheduled task from the configuration file every minute

② configuration file : Set up timed tasks by file mode

③ Configuration Tool crontab: Use to adjust timed tasks

Configuration file format for profile

* * * * * COMMAND

The first *: minutes 0-59,* means to execute every minute

Second *: hours 0-23

Third one *: date 1-31

Fourth one *: month 1-12

Fifth *: week 0-7 (0 or 7 = Sunday)

"Example 1" 21:30 restart Apache per night

* * * Service httpd restart

"Example 2" 1, 10, 22nd of 4:45 restart Apache

1,10,22 * * Service httpd restart

"Example 3" 4:45 restart Apache per month from 1 to 10th

1-10 * * Service httpd restart

"Example 4" restarts Apache every two minutes (no previous conditions)

*/2 * * * * Service httpd restart

"Example 5" odd minutes per hour restart Apache

1-59/2 * * * * Service httpd restart

Start restart at 1 minutes

(even 0-58/2)

"Example 6" from 11 o'clock to 7 a.m., every 1 hours (front conditional) Restart Apache

0 23-7/1 * * * Service httpd restart

Note: Minutes with 0, if used *, means 23 to 7 points any one minute to execute, obviously not the result we want

"Example 7" restarts Apache every 30 minutes from 18:00 to 23:00 daily (with conditions in front)

0,30 18-23 * * * Service httpd restart

Or

0-59/30 18-23 * * * Service httpd restart

Summary

①* means matches at any time.

② can use "a,b,c" to represent A or B or C when executing commands

③ can use a "a-B" to represent a to a/C when executing a command

④ can use "*/a" to execute commands once per A-minute (hour, etc.)

"Use of crontab tools"

Crontab Help Information

Crontab----help

① View a list of scheduled tasks for a user (Dee)

- u Dee

② Modifying a user's (Dee) scheduled task

CRONTAB-E-U Dee

With: Wq save exit (seemingly Ubuntu system exit Edit Schedule task to be more complicated)

③ View the resulting final scheduled task file

-/var/spool/cron

Use

Tail-f/var/log/cron

View Crontan's logs

Linux Scheduled Tasks Crontab notes and summaries (2) Basic composition and configuration of Crontab