Crontab's learning essays

One 、 brief introduction
crontab yes , Instructions for setting up scripts to execute periodically .
Commands are stored in crontab In file

crond Often running in the background , Check every minute if there are scheduled jobs to be performed . This kind of homework is generally called cron jobs. When the operating system is installed , By default, the task scheduling command is started .
Two 、crontab Interpretation of expressions
Command time format :

• * 　  *　  *　  *　　command
  

branch 　 when 　 Japan 　 month 　 Zhou 　 command
The first 1 List minutes 1～59 Per minute * perhaps */1 Express
The first 2 List hours 1～23（0 Express 0 spot ）
The first 3 List date 1～31
The first 4 List month 1～12
The first 5 Column ID week 0～6（0 Sunday ）
The first 6 Column command to run
3、 ... and 、crontab The practice of directives
（1）cron yes linux Built in services for , But it doesn't get up automatically , You can start it in the following way 、 Shut down this service ：
/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 # service crond reload
(2) View the current user crontab Task list for
crontab -l

The list of scheduled tasks is as follows ：

（2） Edit the current user crontab Mission
crontab -e
Input i Enter editing status , take 51-》50

Click on esc
Input shift+“:”– Pay attention to the English status , Input wq Exit the editor

Look again , You can see that the time has changed

Be careful ： The newly created cron Mission , Not immediately , At least 2 It's only in minutes , Of course, you can restart cron Come on, do it right now .
（3） Help order crontab -h

Four 、 Good article
linux Instruction based learning ：https://www.docin.com/p-324829386.html
awk：
https://blog.csdn.net/qq_22253901/article/details/118094440