Shell timed Tasks

1. Know Cron
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, it does not automatically get up, and you can start and shut down this service in the following ways:
/sbin/service Crond Start//Startup service
/sbin/service Crond stop//Shut down service
/sbin/service crond Restart//Text restart service
/sbin/service Crond Reload//Reload Configuration
You can also start the service automatically when the system starts:
At the end of the/etc/rc.d/rc.local script, add:
/sbin/service Crond Start
2. Cron Service
1) Edit directly with crontab command
The Cron service provides the crontab command to set the Cron service, and here are some of the parameters and instructions for this command:
Crontab-u//Set a user's Cron service, which is usually required by the root user when executing this command
CRONTAB-L//list details of a user cron service
Crontab-r//Delete a cron service with no users
CRONTAB-E//Edit a user's cron service
For example, root to view your cron settings: Crontab-u root-l
Again, for example, Root wants to delete Fred's cron settings: Crontab-u fred-r
When editing the Cron service, the edited content has some formatting and conventions, input: Crontab-u root-e
(Note: Eldest brother elder sister, look at the article don't forget to pay attention to me yo, hey)
Enter VI edit mode, the content of the edits must conform to the following format: */1 * * * * ls >>/tmp/ls.txt
The first part of this format is the time setting, the next part is the command to execute, if you want to execute too many commands, you can write these commands into a script, and then call this script directly here, you can recall the full path of the command when the call. Time setting we have a certain agreement, the preceding five * number represents five numbers, the value range and meaning of the numbers are as follows:
Minutes (0-59)
Hours (0-23)
Date (1-31)
Month (1-12)
Week (0-6)//0 on behalf of Sunday
In addition to the numbers there are several special symbols are "*", "/" and "-", ",", * represents all the values within the range of the number, "/" for each meaning, "*/5" means every 5 units, "-" represents from a number to a number, "," separate several discrete numbers. Here are a few examples to illustrate the problem:
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/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
3. Example
I configure cron in the/etc/crontab file;
#product Price Trend Picture
0 1 * * * Root sh/home1/picture/myconfig.sh (executes the root user's/home1/picture/myconfig.sh at 1 o'clock per day)
My myconfig.sh:
Java_home=/home1/jdk1.5.0_03;export Java_home
Java_opts= "-server-djava.awt.headless=true"; export java_opts
(Because my app is a drawing app, so take the above two paragraphs, specify the JDK, etc.)
Cd/home1/picture/lib (Specifies that my jar file is in place)
/home1/jdk1.5.0_03/bin/java-cp/home1/picture/lib/pricetrendpicture.jar:/home1/picture/lib/classes12.jar:/home1 /picture/lib/ibatis-common-2.jar:/home1/picture/lib/ibatis-dao-2.jar:/home1/picture/lib/ibatis-sqlmap-2.jar: Log4j-1.2.8.jar:/home1/picture/lib/xmlparserv2.jar:/home1/picture/lib/commons-logging.jar Com.yesky.run.PriceTrendPicture
/HOME1/JDK1.5.0_03/BIN/JAVA-CP This is my JDK location followed by all the used jar files finally there is the execution class with main ()

Shell Timer Task