Linux Timed Task Example

Source: Internet
Author: User

Basic format:
* * * * * command
Time-sharing Weekly command

The 1th column represents minutes 1~59 per minute with * or */1
The 2nd column represents the hour 1~23 (0 means 0 points)
The 3rd column represents the date 1~31
The 4th column represents the month 1~12
5th Column Identification Number Week 0~6 (0 = Sunday)
6th List of commands to run

Some examples of crontab files:

* * * * */usr/local/etc/rc.d/lighttpd restart
The above example shows that 21:30 restarts Apache per night.

4 1,10,22 * */USR/LOCAL/ETC/RC.D/LIGHTTPD restart
The above example shows that 4:45 restarts Apache on the 1, 10, and 22nd of the month.

1 * * 6,0/USR/LOCAL/ETC/RC.D/LIGHTTPD restart
The above example shows that 1:10 restarts Apache every Saturday and Sunday.

0,30 18-23 * * */usr/local/etc/rc.d/lighttpd restart
The above example shows that Apache restarts every 30 minutes from 18:00 to 23:00 every day.

The above example shows the restart of Apache every Saturday at 11:00am.

* */1 * * * */usr/local/etc/rc.d/lighttpd restart
Restart Apache every hour

* 23-7/1 * * * */usr/local/etc/rc.d/lighttpd restart
From 11 o'clock to 7 in the morning, restart Apache every hour.

0 4 * mon-wed/usr/local/etc/rc.d/lighttpd restart
4th per month with 11-point restart from Monday to Wednesday Apache

0 4 1 Jan */usr/local/etc/rc.d/lighttpd restart
4-point restart of Apache on January 1

Name: crontab

Usage rights: All users

How to use:

crontab file [-u user]-replaces the current crontab with the specified files.

Crontab-[-u user]-replaces the current crontab with standard input.

crontab-1[user]-lists the user's current crontab.

crontab-e[user]-Edit user's current crontab.

crontab-d[user]-Delete the user's current crontab.

Crontab-c dir-Specifies the directory for crontab.

Format of the crontab file: M H d M D cmd.

M: Minutes (0-59).

H: Hours (0-23).

D: Day (1-31).

M: Month (1-12).

D: Day of the Week (0~6,0 is Sunday).

CMD to run the program, the program is fed into sh execution, this shell only user,home,shell these three environment variables


Crontab is used to allow a user to execute a program at a fixed time or at a fixed interval, in other words, a user-like schedule. -u user refers to setting the specified

User's time table, which presupposes that you must have permission (for example, root) to specify another's time schedule. If you do not use the-u user, it means to set the

Set your own schedule.


CRONTAB-E: Do a text editor to set the time table, the default text editor is VI, if you want to use another text editor, please set the VISUAL environment variables first

To specify the use of that text editor (for example, Setenv VISUAL Joe)

Crontab-r: Delete the current schedule table

Crontab-l: List the current schedule

crontab file [-u user]-replaces the current crontab with the specified files.

The format of the schedule table is as follows:

F1 F2 F3 f4 f5 program

Where F1 is expressed in minutes, F2 represents hours, F3 represents the day of the month, F4 represents the month, and F5 represents the day of the one week. program says

The program of the line.

When F1 is * indicates that every minute the program,f2 is executed, the program is executed every hour, and the remainder of the analogy

When the F1 is a-B, it is executed from the time of the minute to the minute of the hour, and the F2 is a-B indicating that it is executed from the first to the first, and the remainder of the analogy

When F1 is */n, it is performed once every n minutes, and F2 is */n for every n-hour interval, with the remainder of the other analogy

When F1 is a, B, C,... A, B, C,... Minutes to execute, F2 for a, B, C,... The time indicated that the first, B, c ... Hours to execute, and the rest of the analogy

The user can also store all the settings in the file file, using the crontab file to set the time schedule.



0 7 * * */BIN/LS

In December, the/usr/bin/backup is performed every 3 hours in the morning from 6 to 12.

0 6-12/3 */usr/bin/backup

Monday to Friday every 5:00 send a letter to [email protected]:

0 * * 1-5 mail-s "HI" [email protected] </tmp/maildata

Every day of the month 0:20 midnight, 2:20, 4:20 .... Perform echo "haha"

0-23/2 * * * echo "haha"


When the program is executed at the time you specify, the system will send you a letter showing what the program is doing, and if you do not wish to receive such a letter, please leave a blank in each line

After adding >/dev/null 2>&1 can be

Example 2:


6 * * * Date


0 */2 * * * Date

#晚上11点到早上8点之间每两个小时, 8 in the morning.

0 23-7/2,8 * * * Date


0 4 * mon-wed date


0 4 1 Jan * Date


$crontab-L lists the user's current crontab.

Linux Timed Task Example

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