What is crontab?

1. Introduction
   Crontab-operate the daemon of each user and the execution schedule.
2. Some parameter descriptions
   Crontab file [-u user]-replace the current crontab with the specified file.
   Crontab-[-u user]-replace the current crontab with the standard input.
   Crontab-1 [user]-list the current crontab of the user.
   Crontab-E [user]-edit the current crontab of the user.
   Crontab-d [user]-delete the current crontab of the user.
   Crontab-C Dir-specifies the crontab directory.
   Crontab file format: m h d m d cmd.
   M: minute (0-59 ).
   H: hour (0-23 ).
   D: Day (1-31 ).
   M: Month (1-12 ).
   D: days in a week (0 ~ 6, 0 is Sunday ).
   The program to be run by CMD is sent to SH for execution. The shell contains only three environment variables: User, home, and shell.
3. The following is an example file:
   # Min hour day month dayofweek command
   #06:10 every morning
   10 6 **** date
   # Every two hours
   0 */2 * Date
   # Every two hours from PM to am, am
   0 23-7/2, 8 **** date
   # Am on the 4th day of each month and from Monday to Wednesday of each week
   0 11 4 * Mon-wed date
   # A.m. of July
   0 4 1 Jan * Date
   Example
   $ Crontab-l list the current crontab of a user.
   # Min hour day month dayofweek command
   10 6 **** date
   0 */2 * Date
   0 23-7/2, 8 **** date