Cron, Cron Jobs, and Crontab

Cron in a Linux/Unix utility/daemon that runs tasks (cron jobs) in the background at regular intervals.
A crontab (cron table) is basically a file that contains the schedule of cron jobs to be run at specific times.

• crontab -l to list the crontab entries
• crontab -e to edit the crontab file
• crontab -r to remove your crontab file

Cron entries use the following syntax:
*     *     *   *    *        command to be executed
-     -     -   -    -
|     |     |   |    |
|     |     |   |    +----- day of week (0 - 6, where Sunday=0)
|     |     |   +------- month (1 - 12)
|     |     +--------- day of month (1 - 31)
|     +----------- hour (0 - 23)
+------------- min (0 - 59)

Entry: Minute when the process will be started [0-60]
Entry: Hour when the process will be started [0-23]
Entry: Day of the month when the process will be started [1-28/29/30/31]
Entry: Month of the year when the process will be started [1-12]
Entry: Weekday when the process will be started [0-6] [0 is Sunday]

* in the minute field means command will be executed every minute.
*/10 means command will be executed every minute. This repeat pattern is not supported by all OS, so better to just use 0,10,20,30,40,50.
You can also use "-" to represent a range of values. For example, 0 1-2 * * * means command will be run at 1am and 2am only.
For readability, you can also use sun, mon, tue, wed, thu, fri, or sat for day of the week. 7 is also acceptable for Sunday.

After editing the crontab, remember to run "service crond reload" to take the new jobs into effect.

Not sure about your crontab syntax? Try crontab.guru.