Linux configuration Crontab

Linux crontab is timed, the following Cron service is the meaning of the timer

Crontab-l List all cron services

CRONTAB-E Modifying the Cron service

Crontab-r Delete Cron Service

1. Questions

You may not be able to modify when using CRONTAB-E, because the default editor for Crontab is Nano

Change to the editor we know

Export editor= "/usr/bin/vim"; Crontab-e

2. Questions

It's also possible that there will be

Send a message to our root This problem occurs/bin/sh:root:command not found

We can see this in the bottom of the mail. X-cron-env: <SHELL=/bin/sh>

The default shell that explains our crontab is/bin/sh

When we see in the Go cat/etc/crontab the setup shell another one, all the shells in the file changed to/bin/sh.

(

In fact, we set in the/etc/crontab can also not consider the above two problems, directly written to/etc/crontab

*/1 * * * * root/opt/bin/test-cron.sh//test.cron.sh scripts executed once per minute

Service cron Restart//restart Crontab

)

In setting the rules for crontab

The rows in the crontab file consist of 6 fields separated by a space or TAB key between the different fields. First 5 fields specify when the command will run
Minutes (0-59)
Hours (0-23)
Date (1-31)
Month (1-12)
Day of the week (0-6, of which 0 stands for Sunday, as if 7 also represents Sunday)
The 6th field is a string to execute at an appropriate time.
Example:
#MIN HOUR Day MONTH DAYOFWEEK COMMAND
#每天早上6点10分
6 * * * Date

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.
Basic format:
* * * * * command
Time-sharing Weekly command
M: Minutes (0-59). Every minute with * or */1
H: Hours (0-23). (0 means 0 points)
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. -u user refers to the setting of the time table for the specified user, 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 setting 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 a different text editor, you first set the VISUAL environment variables to specify the use of the 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 represents the procedure to be executed.
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 add >/dev/null 2>&1 after each line is empty.

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.

/usr/lib/cron/cron.allow indicates who can use the crontab command. If it is an empty file indicates that no one user can schedule the job. If the file does not exist and there is another file/usr/lib/cron/cron.deny, only the user who is not included in the file can use the crontab command. If it is an empty file, it indicates that any user can schedule the job. Two files exist at the same time Cron.allow priority, if none exist, only the Superuser can schedule the job.


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

Example:

Each of the two time values is separated by commas.
In addition to the numbers there are several special symbols that are "*", "/" and "-", ",", * represent all the values within the range of numbers, "/" for each meaning, "*/5&prime;" represents every 5 units, "-" represents a number to a number, "," separate several discrete numbers.


Every morning at 6.

0 6 * * echo "Good morning." >>/tmp/test.txt//Note simply Echo, no output is visible from the screen, because cron emails any output to root.

Every two hours

0 */2 * * echo "has a break now." >>/tmp/test.txt

Every two hours between 11 o'clock and 8 in the morning, eight in the morning.

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

Every month, number 4th and Monday to Sunday, three a.m., 11.

0 4 * 1-3 command line

January 1 morning, 4.

0 4 1 1 * command line

After editing a user's cron settings, Cron automatically generates a file with the same name as the user under/var/spool/cron, and the cron information for this user is recorded in this file, which cannot be edited directly and can only be edited with CRONTAB-E. After Cron starts, read the file once every one of the clocks, and check to see if you want to execute the command inside. Therefore, the Cron service does not need to be restarted after this file has been modified.

2. Edit the/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.


5,15,25,35,45,55 16,17,18 * * command

This means that any day any month, in fact, the daily 4 o'clock in the afternoon, 5 points, 6 points of 5 min, min, min, min, min, min, when the execution of orders.

[Example] in every Monday, three, five 3:00 the system enters the maintenance state and restarts the system. Then the following fields should be written in the crontab file:

* * 1,3,5 shutdown-r +5

Then save the file as Foxy.cron, and then type crontab foxy.cron to install the file.

[Example] 10 minutes per hour, 40 minutes execute the Innd/bbslin in the user directory:

10,40 * * * * Innd/bbslink

[Example] 1 minutes per hour execute the bin/account command in the user directory:

1 * * * * bin/account

[Example] every day 3:20 A.M. executes two instructions (each instruction is separated) as follows in the user directory:

3 * * * (/bin/rm-f expire.ls logins.bad;bin/expire$#@62;expire.1st)

[Example] every year in January and April, 4th to 9th 3:12 and 3:55 execute/bin/rm-f expire.1st This command, and add the results after mm.txt this file (mm.txt file is located in the user's own directory location).

12,55 3 4-9 1,4 */bin/rm-f expire.1st$#@62;$#@62;mm.txt

[Example] Let's look at a crontab file for a super User:

#Run the ' Atrun ' program every minutes

#This runs anything that's due to run from the ' at '. See mans ' at ' or ' atrun '.

0,5,10,15,20,25,30,35,40,45,50,55 * * * */usr/lib/atrun

7 * * * updatedb

8,10,22,30,39,46,54,58 * * * */bin/sync

　　

Linux configuration Crontab