Crontab is a utility on the CentOS operating system that allows you to schedule recurring tasks at a predetermined time. Here are instructions for using crontab on CentOS:
Step 1: Open crontab for the current user
To open crontab for the current user, run the following command:
crontab -e
Step 2: Understand the crontab syntax
Each line in the crontab represents a specific scheduled task.
The crontab syntax is as follows:
* * * * * command_to_be_executed
- - - - -
| | | | |
| | | | ----- Day of the week (0 - 7) (Sunday is 0 and 7)
| | | ------- Month (1 - 12)
| | --------- Day of the month (1 - 31)
| ----------- Hour (0 - 23)
------------- Minute (0 - 59)
The asterisk (*) means all possible values for that field.
Step 3: Define tasks in the crontab
For example, to run a script named "myscript.sh" at 1 AM every day, add the following line to the crontab:
0 1 * * * /path/to/myscript.sh
Step 4: Save and exit
After adding tasks to the crontab, save and exit by pressing Ctrl + X, then type Y and press Enter.
Step 5: View crontab
To view the list of tasks in the crontab, run the following command:
crontab -l
Step 6: Remove a task from the crontab
o remove a task from the crontab, run the following command:
crontab -r
Note: Be careful when using crontab, ensure the syntax and scheduling time are correct to avoid system malfunction or overload.