Linux crontab scheduled execution of task command format

Recurring Task Execution: Cron, Vixie-cron,cronie

Crond:cron Daemon, cron Daemon, always working in the background

#service crond Status

Crond (PID 1718) is running ...

If the status information is "is stopped.", you need to perform "service Crond start;chkconfig crond on";

Cron tasks are divided into two categories:

system cron: defined in/etc/crontab

user cron: defined in the/var/spool/cron directory, each user has a file with the same name as the user name, which functions like/etc/crontab

Each row defines a separate task:

Shell=/bin/bash

Path=/sbin:/bin:/usr/sbin:/usr/bin

Mailto=root

home=/

      # Environment Variables

#For details see Mans 4 Crontabs

#Example of Job Definition:

#.----------------Minute (0-59)

      #| .-------------Hour (0-23)

       #|    

       #|      

       #|        

       #|        

       #*   *      

Note: If the task defined in Cron is a script, each command in this script follows the CRON PATH environment variable definition, so it is not necessary to test the problem-free script on the command line;

Solution: 1 , command use absolute path 2. Start your own definition of a dedicated PATH environment variable in the script

Each job of the user cron consists of 2 parts

Time

minutes, hours, days , months , weeks .

Command

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.
0 * * 6/USR/LOCAL/ETC/RC.D/LIGHTTPD restart
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
Description
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. -uuser 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.
Parameters:
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 (e.g. Setenv Visualjoe)
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.
Example:
#每天早上7点执行一次/bin/ls:
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"
Attention:
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:
#每天早上6点10分
6 * * * Date
#每两个小时
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
#每个月的4号和每个礼拜的礼拜一到礼拜三的早上11点
0 4 * mon-wed date
#1月份日早上4点
0 4 1 Jan * Date
Example
$crontab-L lists the user's current crontab.

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Linux crontab scheduled execution of task command format