Question 1

What is a cron expression?

Accepted Answer

A cron expression is a string of 5 space-separated fields used to schedule automated tasks on Unix/Linux systems and cloud platforms. The fields represent: minute (0–59), hour (0–23), day of month (1–31), month (1–12), and day of week (0–7, where 0 and 7 both mean Sunday). The asterisk (*) wildcard means 'every'. For example, '0 9 * * 1-5' runs a job at 9:00 AM every weekday (Monday through Friday).

Question 2

What does '* * * * *' mean in cron?

Accepted Answer

The expression '* * * * *' means run every minute, of every hour, of every day, of every month, on every day of the week. It is the most frequent cron schedule possible and equates to 1,440 executions per day. It is commonly used for health checks, monitoring scripts, or real-time data polling jobs.

Question 3

How do I run a cron job every 5 minutes?

Accepted Answer

Use the expression '*/5 * * * *'. The forward slash (/) is the step operator. '*/5' in the minute field means starting from minute 0, run every 5 minutes (0, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55). This runs 12 times per hour and 288 times per day.

Question 4

What cron expression runs a job daily at midnight?

Accepted Answer

The expression '0 0 * * *' runs a job once daily at exactly midnight (00:00). The '0' in the minute field and '0' in the hour field pin the execution to the start of midnight. Some cron implementations also accept the special string '@daily' as an equivalent alias.

Question 5

What is the difference between cron and crontab?

Accepted Answer

Cron is the daemon (background service) that reads schedules and executes commands at the specified times. Crontab (cron table) is the configuration file that stores the list of cron jobs. You manage crontab entries using 'crontab -e' to edit, 'crontab -l' to list, and 'crontab -r' to remove all scheduled jobs for your user.

Question 6

How do I schedule a cron job to run only on weekdays?

Accepted Answer

Use '0 9 * * 1-5' to run at 9 AM on weekdays (Monday=1 to Friday=5). The last field (day of week) accepts ranges with a hyphen. To run only on weekends, use '0 9 * * 6,0' (Saturday=6, Sunday=0). For a specific weekday like every Monday, use '0 9 * * 1'.

Question 7

What are the special cron strings like @daily and @weekly?

Accepted Answer

Many cron implementations support special shorthand strings: @reboot (run once at startup), @yearly or @annually (run once a year, '0 0 1 1 *'), @monthly (run once a month, '0 0 1 * *'), @weekly (run once a week on Sunday, '0 0 * * 0'), @daily or @midnight (run once a day, '0 0 * * *'), and @hourly (run once an hour, '0 * * * *').

Question 8

How do I use cron expressions in AWS EventBridge, GitHub Actions, or Google Cloud Scheduler?

Accepted Answer

AWS EventBridge uses a 6-field cron format: 'cron(minute hour day month weekday year)'. GitHub Actions uses standard 5-field cron in the 'schedule' trigger under 'on'. Google Cloud Scheduler also uses standard 5-field unix-cron format. Kubernetes CronJobs use standard 5-field cron. This tool generates standard 5-field cron expressions compatible with most platforms.

Expression	Meaning	Schedule
	Every minute	1,440×/day
	Every hour	24×/day
	Daily midnight	1×/day
	Weekdays 9 AM	5×/week
	Weekly Sunday	1×/week
	Monthly 1st	1×/month
	Every 5 min	288×/day
	Twice daily	2×/day

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