crontab  -e  [username]   Edit a copy of the user's crontab file,    
                                or create an empty file to edit if the       
                                crontab file does not exist. When editing    
                                is complete, the file will be copied into    
                                the crontab directory as the user's          
                                crontab file.                                
                                                                                
      crontab  -l  [username]   Lists the user's crontab file.             
                                                                                
      crontab  -r  [username]   Remove the user's crontab file from the    
                                crontab directory.