Question 1

What are the 5 standard POSIX crontab fields?

Accepted Answer

In order from left to right: (1) Minute (0–59), (2) Hour (0–23), (3) Day of the Month (1–31), (4) Month (1–12 or JAN–DEC), and (5) Day of the Week (0–6 or SUN–SAT, where 0 and 7 both represent Sunday).

Question 2

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

Accepted Answer

POSIX cron uses 5 fields with minute precision. Java Quartz, AWS EventBridge, and Spring cron often use 6 or 7 fields (starting with seconds 0–59, and optionally including a Year field). This generator builds standard 5-field POSIX crontab syntax used by Linux/Unix cron daemons, Kubernetes CronJobs, and GitHub Actions.

Question 3

What are cron shorthand presets like @daily, @hourly, and @reboot?

Accepted Answer

Shorthand aliases replace standard 5-field numbers: @yearly / @annually (0 0 1 1 *), @monthly (0 0 1 * *), @weekly (0 0 * * 0), @daily / @midnight (0 0 * * *), @hourly (0 * * * *), and @reboot (runs once on daemon startup).

Question 4

How do day-of-month and day-of-week interact in cron schedules?

Accepted Answer

When both day-of-month (field 3) and day-of-week (field 5) are specified with non-wildcard values, POSIX cron daemons use a logical OR condition. The job executes whenever either condition is met (e.g., 0 0 15 * 5 runs on the 15th of the month AND every Friday).

Question 5

How do you schedule a cron job to run every N hours or minutes?

Accepted Answer

Use the step slash (/) operator. To run every 2 hours: 0 */2 * * *. To run every 15 minutes: */15 * * * *. Step values increment from the beginning of the field range (e.g., */2 in hours fires at 0, 2, 4, 6, 8, 10, 12, 14, 16, 18, 20, 22).

Question 6

What timezone does a cron job execute in?

Accepted Answer

A crontab job executes in the local timezone of the host server running the cron daemon (crond). Cloud platforms (AWS, GCP) and Docker containers default to UTC. Ensure your server clock matches your expected fire schedule or set the CRON_TZ environment variable if supported by your cron daemon.

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