linux Timer crontab usage :

1、 The basic 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

2、 Create timer crontab -e, For example, the input :

30 2 1 * * /usr/bin/certbot renew >> /var/log/le-renew.log
35 2 1 * * /usr/bin/systemctl reload nginx

If you don't need to fill in the options, write * , You can't leave it empty, or you'll report an error , for example :

"/tmp/crontab.cNLTYQ":1: bad month
errors in crontab file, can't install

3、crontab -l Check the timer content set by the system

4、 Location of timer file :/var/spool/cron

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