Detailed and sample crontab in Linux (collection)

Mar 10 posted in OS (RSS), comments.

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cron is timing the implementation of a tool under linux, without human intervention in the case of running jobs. Cron is built as a Linux service, but it does not automatically up, you can use the following methods to start, shut down the service:

/ Sbin / service crond start / / start service
/ Sbin / service crond stop / / close service
/ Sbin / service crond restart / / restart services
/ Sbin / service crond reload / / reload the configuration

You can also start the service automatically when the system starts:
In the / etc / rc.d / rc.local added at the end of this script:
/ Sbin / service crond start

Cron is now inside the service has been in the process, we can use the service of, Cron service provides the following interfaces for your use:

1, directly edit the crontab command

cron service providers to set the cron crontab command service, the following are some of the parameters of this command and description:

crontab-u / / set a user's cron service, usually root user running this command, this parameter needs
crontab-l / / a user cron service listed the details of
crontab-r / / remove a user's cron service
crontab-e / / edit a user's cron service

For example, set the root to see your cron: crontab-u root-l
For another example, root to delete the cron setting fred: crontab-u fred-r
When editing the cron service, edit the contents of some of the formats and conventions, enter: crontab-u root-e
Enter vi edit mode, edit the content must meet the following format: * / 1 * * * * ls>> / tmp / ls.txt

The first part of this format is the time set, the back part of the command to execute if the command to execute too many, you can write these commands inside a script, then here you can directly call the script, and call when I remember to write the full path to the command. Time setting we have some agreement, on behalf of the previous five * number five figures, the range and number of meanings are as follows:

Minutes (0-59)
Hours (0-23)
Date (1-31)
Month (1-12)
Week (0-6) / / 0 for Sunday

In addition there are several numbers is a special symbol and "-",",",* "*","/" behalf of all the range of numbers, "/" represents the meaning of each "* / 5 "said the five units," - "represents a number from a number to," "separated a few discrete numbers. The following few examples illustrate the problem:

6 o'clock every morning

0 6 * * * echo "Good morning.">> / Tmp / test.txt / / Note that simply echo, not see any output from the screen, because the cron output to email to any mailbox of root.

Every two hours

0 * / 2 * * * echo "Have a break now.">> / Tmp / test.txt

11 pm to 8 am every two hours between the morning and eight

0 23-7/2, 8 * * * echo "Have a good dream:)">> / tmp / test.txt

4th of every month and every week the morning of Monday to Wednesday 11

0 11 4 * 1-3 command line

January 1, 4:00 am

0 4 1 1 * command line

Every time you edit a user's cron settings, cron automatically in / var / spool / cron to generate a file with the same name as the user, this user information recorded in the cron file, this file can not directly edit , and can only use the crontab-e to edit. cron is started every time a bell read this file to check whether to execute the command inside. This file is modified so no need to restart the cron service.

2, edit / etc / crontab cron configuration file

cron service not only to read once per minute / var / spool / cron all the files, but also read an / etc / crontab, so we can configure this file using cron service to do something. Use crontab configuration for a user, and edit / etc / crontab for system tasks. This file format is:

SHELL = / bin / bash

PATH = / sbin: / bin: / usr / sbin: / usr / bin

MAILTO = root / / If an error occurs, or a data output, data as e-mail sent to this account

HOME = / / / the user running path, here is the root directory

# Run-parts

01 * * * * root run-parts / etc / cron.hourly / / hourly / etc / cron.hourly the script
02 4 * * * root run-parts / etc / cron.daily / / perform daily / etc / cron.daily script within
22 4 * * 0 root run-parts / etc / cron.weekly / / execute each week / etc / cron.weekly the script
42 4 1 * * root run-parts / etc / cron.monthly / / month to perform the / etc / cron.monthly the script

Attention to "run-parts" of this argument, if this parameter is removed, then later you can write a script to run the name of the folder name rather than a.

--------------------------------------
Basic format:
* * * * * Command
Time-moon week command

Section 1 of minutes from 1 to 59 per minute with a * or * / 1 means that the first two hours of 1 to 23 (0 0)
Column 3 represents the date from 1 to 31
Section 4 of the month from 1 to 12
Section 5 identifies the number of weeks 0 to 6 (0 for Sunday)
Section 6 of the command to run

Some examples of the crontab file:

30 21 * * * / usr / local / etc / rc.d / lighttpd restart
The above example that night 21:30 to restart lighttpd.

45 4 1,10,22 * * / usr / local / etc / rc.d / lighttpd restart
The above example shows the monthly 1,10,22 Day 4:45 to restart lighttpd.

10 1 * * 6,0 / usr / local / etc / rc.d / lighttpd restart
The above examples show every Saturday, Sunday 1:10 to restart lighttpd.

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

0 23 * * 6 / usr / local / etc / rc.d / lighttpd restart
The above example that every Saturday the 11: 00 pm to restart lighttpd.

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

* 23-7/1 * * * / usr / local / etc / rc.d / lighttpd restart
11 pm to 7 am, between every hour restart lighttpd

0 11 4 * mon-wed / usr / local / etc / rc.d / lighttpd restart
Monthly on the 4th and Monday to Wednesday 11:00 to restart lighttpd

0 4 1 jan * / usr / local / etc / rc.d / lighttpd restart
January 1 to 4:00 lighttpd restart