A, at a one-time task settings
using the scheduled tasks at command is only executed once at the specified time, provided that the corresponding system must be at the service has been running.
For example, we set the task to perform at 2019-8-26 18:40.
To remember the time of execution of the task to verify the results.
To that when we make a mistake or do not want the job then how should we do it? This time we need to use the command atrm.
Two, crontab periodic task set
crontab configuration file
Use the crontab command to manage a user's scheduled tasks
after use "crontab -e", will open the scheduled task editing interface.
After entering the task editing interface can add their own scheduled task we want to perform configuration.
Here we add in a task configuration.
When we do not want to use "crontab -r" when performing these tasks planned for emptying, if when we want to delete a specific scheduled task by "crontab -e" to enter the task editing interface to delete.