Debian's timed execution command crontab
2012-12-3 5:50 Category: NAS 2743 views 1 reviews Tags:LinuxDebian
Debian's timed execution command crontab, which corresponds to a scheduled task for Windows
If you want Debian to execute commands on a regular basis, crontab!
It functions like Microsoft's scheduled tasks and can execute the commands you want at the time you set.
By writing a setup file, you can combine complex execution times to make the execution of the command more efficient.
The location of the cron settings file under the Debian system
/etc/crontab
The general contents are as follows:
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#/etc/crontab:system-wide Crontab
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# Unlike any and crontab you don ' t has to run the ' crontab '
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# command to install the new version when you edit this file.
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# This file also have a username field, that's none of the other crontabs do.
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Shell=/bin/sh
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Path=/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin
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# m H Dom Mon Dow user command
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* * * * * Root run-parts--report/etc/cron.hourly
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6 * * * Root test-x/usr/sbin/anacron | | Run-parts--report/etc/cron.daily
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6 * * 7 root test-x/usr/sbin/anacron | | Run-parts--report/etc/cron.weekly
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6 1 * * Root test-x/usr/sbin/anacron | | Run-parts--report/etc/cron.monthly
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0 1 * * root/usr/bin/updatedb
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#
What you need to set is the # m H Dom Mon Dow user command section below
The corresponding meaning from left to right is:
0-59 hours 0-23 Days January-3 January 1-12 weeks 0-7 user commands for executing commands
One of the more interesting is: week, 0 and 7 are all on behalf of the Sunday
and the special symbols that can be used are
* (asterisk) represents all time accepted
, (comma) represents the number of values that the same classification can have
-(minus sign) represents the execution during this time period
/n represents once every n times
Example:
* * * command: <em> daily 12:30 Execution command</em>
0 6,12 * * command:<em> 6:00 and 12:00 per month of 15th, executed command</em>
8 1-15 6 * command:<em> per year June 1 to 15th 8:10 execution command</em>
*/5 * * 7 command: <em> Sunday command</em> every five minutes
Timer Syntax:
Is the first part of the above-planned task. It determines when to execute a scheduled task.
It consists of 5 parts:
1. Minutes (0-59)
2. Hours (0-23)
3. What day of one months (1-31)
4. Which month of the year (1-12)
5. Day of the week (0 is Sunday)
Asterisks if a section appears with an asterisk instead of a number, it means that the time represented by this part is all performed.
It may not be easy to speak clearly at the moment, so look at the example.
Example:
1, the following scheduled tasks will continue to run
* * * * * * [command]
2. The following scheduled tasks will run at 0 ticks per hour (that is, hourly execution)
0 * * * * [command]
3. The following is still a scheduled task that runs hourly. But it runs at a quarter of an hour (1:15,2:15 ... ）
* * * * * [command]
4, the following scheduled tasks are performed once a day, at 2:30 minutes
2 * * * [command]
5. The following scheduled tasks are performed at midnight 2nd on each month (for example: February 2, 2010 00:00)
0 0 2 * * [command]
6. The following scheduled tasks will be performed at 0 minutes per hour every Monday
0 * * * 1 [command]
7, the following will run 3 times per hour, in 0 minutes, 10 points, and 20 ticks
0,10,20 * * * * [command]
8, the following is used division sign "/" to indicate how many times each run.
*/5 * * * * [command] runs every 5 minutes
*/2 * * * [command] run every 2 hours (* */2 * * * [command] this is wrong! )
*/1 * * * * root wget-o/var/log/cron.txt http://www.592.net/test.php every minute to visit a PHP script, check if PHP is automatically running every minute, can view Var/log/cro N.txt file, see if there is a website PHP back to the content on it!
9, you can also use "-" to indicate a range, as follows 5 to 10 points of each hour to run
0 5-10 * * * [command]
10, there is also a special time keyword "@reboot", that is, each time you restart the server to run a scheduled task
@reboot [command]
Set up and manage scheduled tasks
Edit Crontab to set up a scheduled task. Using the following command, the crontab content is opened in VI for editing:
Crontab-e
If you only want to see and do not need to edit, you can use the following command
Crontab-l
To delete the contents of the crontab, delete all the scheduled tasks, so you can:
Crontab-r
Cron is a timed execution tool under Linux that can run a job without human intervention. Since Cron is a built-in service for Linux, he does not automatically get up and can start and close the service in the following ways:
Edit/etc/crontab File Configuration cron
Cron service every minute not only to read all the files within/var/spool/cron, but also to read a/etc/crontab, so we configure this file can also use the Cron service to do something. The crontab configuration is for a user, while the edit/etc/crontab is a task for the system. The file format for this file is:
Shell=/bin/bash
Path=/sbin:/bin:/usr/sbin:/usr/bin
Mailto=root//If an error occurs, or if there is data output, the data is sent to this account as an email
home=///user-run path, here is the root directory
# Run-parts
* * * * * root run-parts/etc/cron.hourly//hourly execution of scripts within/etc/cron.hourly
4 * * * Root run-parts/etc/cron.daily//daily execution of scripts within/etc/cron.daily
4 * * 0 root run-parts/etc/cron.weekly//weekly execution of scripts within/etc/cron.weekly
4 1 * * Root run-parts/etc/cron.monthly//monthly to execute scripts within/etc/cron.monthly
Attention to the "run-parts" This parameter, if you remove this parameter, you can later write to run a script name, not the folder name.
Restart command:
Debian
/etc/init.d/cron restart
Linux
/etc/rc.d/init.d/crond restart
Linux Autorun Script Parameters Introduction
