After entering the Linux system, first check whether the Crontab service is installed
Check if the crontab tool is installed crontab -l
Check if the Crontab service is started service crond status
If not installed, install cron
yum install vixie-cron
yum install crontabs
Service Operation Instructions:
/sbin/service crond start //Start the service
/sbin/service crond stop //Close the service
/sbin/service crond restart //Restart the service
/sbin/service crond reload //Reload configuration
/sbin/service crond status //Start the service
Write a timed task, if there is no timed task
Tips are as follows: no crontab for root
Write the task crontab -e (print the current time to the log file log.txt every minute)
*/1 * * * * date >> /tmp/log.txt
Prompt to view the timing task tail -f /tmp/log.txt (continuously display the contents of several lines of the file, dynamic; -3 represents the last 3 lines)
[root@localhost ~]# tail -f /tmp/log.txt Mon Jul 10 17:19:01 CST 2017 Mon Jul 10 17:20:01 CST 2017 Mon Jul 10 17:21:01 CST 2017 Mon Jul 10 17:22:01 CST 2017 Mon Jul 10 17:23:01 CST 2017 Mon Jul 10 17:24:01 CST 2017 Mon Jul 10 17:25:01 CST 2017 Mon Jul 10 17:26:01 CST 2017 Mon Jul 10 17:27:01 CST 2017 Mon Jul 10 17:28:01 CST 2017 Mon Jul 10 17:29:01 CST 2017 Mon Jul 10 17:30:01 CST 2017 Mon Jul 10 17:31:01 CST 2017
Crontab basic composition
Format of the Crontab Configuration File
*Represents not specified, that is, it must be executed at all times, that is, every minute, every hour, every day, etc.
Common cases are as follows
Restart apache every night at 21:30
30 21 * * * service httpd restart
restarts apache at 4:45 on the 1st, 10, 22nd of every month
45 4 1,10,22 * * service httpd restart
restarts apache at 4:45 on the 1st to the 10th of every month
45 4 1- 10 * * service httpd restart
restarts the apache server every two minutes
*/2 * * * * service httpd restart #even minutes
1-59/2 * * * * service httpd restart #base minutes
between 11pm and 7am , restart apache every hour
0 23-7/1 * * * service httpd restart
every 30 minutes between 18:00 and 23:00 restart apache
0,30 18-23 * * * service httpd restart
0-59 /30 18-23 * * * service httpd restart
runs the test.php file in the root directory every minute
*/1 * * * * /usr/local/php/bin/php /data/wwwroot/door/test.php
Summary:
* means match at any time,
you can use A,B,C to mean or execute a command when A or B or C
can use AB to mean between A and B to execute a command
You can use */A to mean every A minute (hour, etc.) Execute the command
crontab -l to view the scheduled tasks
crontab -e create and edit the scheduled tasks (delete a single one can enter the edit manual deletion)
crontab -r delete all the scheduled tasks
service crond restart restart all the scheduled tasks