Crontabs can be used to configure specific tasks to be run at designated times.

Quick Links:
Crontab Format
View running crontabs
Crontab examples for better understanding

Format

To view the format of crontabs you can read the file /etc/crontab

minute   hour   day   month   dayofweek   command
  *        *     *      *       *

The diagram below shows a little more detail into the parameters of each column

*     *     *   *    *        command to be executed
-     -     -   -    -
|     |     |   |    |
|     |     |   |    +----- day of week (0 - 6) (Sunday=0)
|     |     |   +------- month (1 - 12)
|     |     +--------- day of        month (1 - 31)
|     +----------- hour (0 - 23)
+------------- min (0 - 59)

Viewing configured crontabs

You can use the following command to see the configured cronjobs on the server:

crontab -e

Example Crontabs

min   hour   day   month   dayofweek   [command]

30    0      1    1,6,12     *    [0:30 Hrs  on 1st of Jan, June & Dec]
10    4      1      *        *     [1st of every month @ 4:10]