Cron

Cron is a time-based job scheduler in Unix-like operating systems.
Automating recurring tasks, such as automated file backups, script execution, or application launching post-boot etc. is managed in Linux via the cron system daemon.

• The cron Process: A background service initialized during the system boot sequence that continuously monitors the system time and executes scheduled automation tasks.
• The crontab (Cron Table): A specialized text configuration file containing a structured list of commands scheduled to run at specific time intervals.

The crontab configuration can be edited using the crontab -e command

Crontab Syntax & Time Fields#

A crontab entry requires exactly six fields written sequentially on a single line. The first five fields define the precise time execution criteria, while the sixth field defines the targeted command string.

 .---------------- minute (0 - 59)
 |  .------------- hour (0 - 23)
 |  |  .---------- day of month (1 - 31)
 |  |  |  .------- month (1 - 12)
 |  |  |  |  .---- day of week (0 - 6) (Sunday to Saturday)
 |  |  |  |  |
 *  *  *  *  *  /path/to/command_or_script

Syntax Field Descriptions#

3. Advanced Time Operators & Execution Syntax#

Crontabs support specialized operators to create complex, periodic time frequencies without requiring absolute, explicit static integers.

Wildcards and Step Intervals#

• The Asterisk (*) Wildcard: Acts as a “don’t care” value. When placed in a field, the command evaluates as matching every possible increment within that field’s scope (e.g., an asterisk in the MON field means execution happens every single month).
• The Step Operator (/): Specifies a step increment value across a range. For instance, pairing the wildcard with a step operator in the hour field (*/12) dictates execution strictly every twelve hours.