Question 1

What is cron?

Accepted Answer

Cron is a time-based job scheduler in Unix-like systems. It reads a crontab file and executes commands at specified times defined by cron expressions.

Question 2

What is the difference between 5-field and 6-field cron?

Accepted Answer

Standard 5-field cron is: minute hour dom month dow. 6-field cron (Spring @Scheduled, AWS) adds a seconds field at the start: second minute hour dom month dow.

Question 3

What do the special characters * / - , mean?

Accepted Answer

* means any value. / means step (*/5 = every 5). - means range (1-5 = 1 through 5). , means list (1,3,5 = at 1, 3, and 5).

Question 4

What are common cron patterns?

Accepted Answer

Every minute: * * * * *. Every hour: 0 * * * *. Every midnight: 0 0 * * *. Every 5 minutes: */5 * * * *. Weekdays 9am: 0 9 * * 1-5.

Question 5

Does cron handle timezones?

Accepted Answer

Standard crontab uses the system timezone. AWS EventBridge and GitHub Actions allow specifying timezone in schedule expressions. Always verify which timezone your cron daemon uses.

Question 6

What is the difference between cron and crontab?

Accepted Answer

Cron is the daemon that runs scheduled jobs. Crontab (cron table) is the configuration file that defines which commands to run at which times.

Question 7

What is the maximum cron frequency?

Accepted Answer

Standard cron has a minimum interval of 1 minute (* * * * *). For sub-minute scheduling, use systemd timers, a job queue, or sleep loops within the cron job itself.

Question 8

What happens when both DOM and DOW are specified?

Accepted Answer

When both day-of-month and day-of-week are non-wildcard, most implementations (including Vixie cron) execute the job when EITHER condition is satisfied, not both.

Cron 파서