1. Schematic diagram of the principle:
2. crond task scheduling
crontab to set up scheduled tasks.
3. Overview
Task scheduling: refers to a specific command or program that the system executes at a certain time.
Task scheduling classification: 1. System work: Some important work must be performed in cycles. such as virus scanning
2. Individual user work: Individual users may wish to perform certain procedures, such as backups of the mysq| database.
4. Basic grammar
crontab [options]
4.1. Common options
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-e
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Edit crontab timed tasks
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-l
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Query crontab tasks
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-f
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Delete all crontab tasks of the current user
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5. Quick Start
5.1. Task requirements
Set the task schedule file: /etc/crontab
Set up a personal schedule. Execute the crontab -e command
Then enter the task into the schedule file
Such as: */1****ls -l /etc/>/tmp/to.txt
It means to execute the ls -l /etc/ >/tmp/to.txt command every minute of every hour
5.2, the steps are as follows
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cron -e
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* / 1 **** ls -l /etc/>/tmp/to.txt
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It takes effect after saving and exiting
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ls -l /etc/ > /tmp/to.txt is automatically invoked every minute
5.3. Parameter details
6. Several application examples of task scheduling
Case 1: Append the current date information to the /tmp/mydate file every minute
1) First write a file mytask1.sh
date >> /tmp/mydate
2) Give mytask1.sh an executable permission
chmod 744 /home/mystask1.sh
3）crontab -e
4）*/1**** /home/mytask1.sh
5) Success
Case 2: Append both the current date and the calendar to the /home/mycal file every minute
1) First write a file mytask2.sh
date >> /tmp/mycal
cal >> /tmp/mycal
2) Give mytask2.sh an executable permission
chmod 744 /home/mystask2.sh
3）crontab -e
4）*/1**** /home/mytask2.sh
5) Success
Case 3: Backup the mysql database testdb to the file mydb.bak at 2:00 am every day.
1) First write a file mytask3.sh
/usr/local/mysql/bin/mysqldump -uroot -proot testdab >/tmp.mydb.bak
2) Give mytask2.sh an executable permission
chmod 744 /home/mystask3.sh
3）crontab -e
4）0 2 *** /home/mytask3.sh
5) Success
7. Crontab related commands:
1) crontab -r: Terminate task scheduling.
2) crontab -l: List which tasks are currently scheduled.
3) service crond restart [restart task scheduling]