# crontab –e
Enter and edit the user-defined crontab configuration file, it will be written to the /var/spool/cron directory, and a file with the same user name will be generated. The content of the file is the timing script we edited.
# vi /etc/crontab
Enter the system's crontab configuration file
Format of the crontab file:
{minute} {hour} {day-of-month} {month}{day-of-week} {full-path-to-shell-script}
o minute: the range is 0 – 59
o hour: the range is 0 – 23
o day-of-month: the range is 0 – 31
o month: The range is 1 – 12. 1 is January . 12 is December .
o Day-of-week: The range is 0 – 7. Sunday can be 0 or 7.
Example: 00 * * * /XXX/XXXX/XXXXXXXX.sh
This will run the specified .sh file every morning
Valid options for crontab :
crontab - e : Modify the crontab file . If the file does not exist, it will be created automatically.
crontab -l : Display the crontab file.
crontab -r : Delete the crontab file.
crontab -ir : Alert the user before deleting the crontab file.