Question 1

What is a cron expression?

Accepted Answer

A cron expression is a string of five (or six) fields separated by spaces that defines a schedule for automated tasks. The fields represent minute, hour, day of month, month, and day of week. For example, '0 9 * * 1' means 'every Monday at 9:00 AM'.

Question 2

How do I read a cron schedule?

Accepted Answer

Read a cron expression left to right: the first field is minute (0–59), the second is hour (0–23), the third is day of month (1–31), the fourth is month (1–12), and the fifth is day of week (0–7, where both 0 and 7 are Sunday). An asterisk (*) means 'every' for that field.

Question 3

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

Accepted Answer

'* * * * *' means the job runs every minute of every hour of every day — the most frequent possible cron schedule. It is often used for testing or for tasks that must run continuously at one-minute intervals.

Question 4

How do I run a cron job every 5 minutes?

Accepted Answer

Use the expression '*/5 * * * *'. The '*/5' in the minutes field means 'every 5 minutes' (i.e., at 0, 5, 10, 15 … 55). The remaining asterisks mean every hour, every day, every month, and every day of the week.

Question 5

What is the difference between cron and crontab?

Accepted Answer

Cron is the background service (daemon) that executes scheduled tasks on Unix/Linux systems. Crontab (cron table) is the configuration file where you define those scheduled tasks using cron expressions. You edit your crontab with the 'crontab -e' command.

Field	Values	Allowed Special Chars	Examples
Second (6/7-field)	0–59	* , - /	0, */10, 30
Minute	0–59	* , - /	0, */5, 15,45
Hour	0–23	* , - /	0, 9-17, */6
Day of Month	1–31	* , - /	1, 15, L
Month	1–12	* , - /	1, JAN, */3
Day of Week	0–7	* , - /	0=Sun, 1-5=Weekdays
Year (7-field)	1970–2099	* , - /	2024, 2025-2030

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