Understanding Cron Syntax: Schedule Tasks Like a Pro

Cron is the standard task scheduler on Unix-like systems, and cron expressions are used everywhere — Linux crontabs, GitHub Actions, Kubernetes CronJobs, AWS EventBridge, and CI/CD pipelines. The syntax looks cryptic at first, but it follows a simple pattern. This guide covers everything from basic schedules to advanced expressions.

Cron Expression Format

A standard cron expression has five fields separated by spaces:

┌───────────── minute (0-59)
│ ┌───────────── hour (0-23)
│ │ ┌───────────── day of month (1-31)
│ │ │ ┌───────────── month (1-12)
│ │ │ │ ┌───────────── day of week (0-7, where 0 and 7 = Sunday)
│ │ │ │ │
* * * * *

Field	Values	Special Characters
Minute	0-59	* , - /
Hour	0-23	* , - /
Day of month	1-31	* , - / L W
Month	1-12 or JAN-DEC	* , - /
Day of week	0-7 or SUN-SAT	* , - / L #

Special Characters

Character	Meaning	Example
*	Any value	* * * * * = every minute
,	Value list	1,15 * * * * = minute 1 and 15
-	Range	1-5 * * * * = minutes 1 through 5
/	Step	*/15 * * * * = every 15 minutes
L	Last	0 0 L * * = last day of month
W	Nearest weekday	0 0 15W * * = nearest weekday to the 15th
#	Nth day of week	0 0 * * 5#3 = third Friday

Note: L, W, and # are extensions not available in all cron implementations. Standard Unix cron supports * , - / only.

20 Practical Examples

Basic Intervals

# Every minute
* * * * *

# Every 5 minutes
*/5 * * * *

# Every 15 minutes
*/15 * * * *

# Every hour (at minute 0)
0 * * * *

# Every 30 minutes
0,30 * * * *

Specific Times

# Every day at midnight
0 0 * * *

# Every day at 9:00 AM
0 9 * * *

# Every day at 2:30 PM
30 14 * * *

# Twice a day (9 AM and 5 PM)
0 9,17 * * *

# Every day at 6 AM, 12 PM, and 6 PM
0 6,12,18 * * *

Day-Specific Schedules

# Every Monday at 9 AM
0 9 * * 1

# Weekdays at 8 AM (Mon-Fri)
0 8 * * 1-5

# Weekends at 10 AM
0 10 * * 0,6

# First day of every month at midnight
0 0 1 * *

# Every quarter (Jan, Apr, Jul, Oct) on the 1st at midnight
0 0 1 1,4,7,10 *

Complex Schedules

# Every weekday during business hours (every 30 min, 9 AM - 5 PM)
*/30 9-17 * * 1-5

# Every Sunday at 2 AM (weekly backup)
0 2 * * 0

# Every 6 hours
0 */6 * * *

# Last day of every month at 11:59 PM (requires L support)
59 23 L * *

# Every 10 minutes during business hours on weekdays
*/10 9-17 * * 1-5

Six-Field Cron (With Seconds)

Some systems (Spring, Quartz, AWS) support a sixth field for seconds:

┌───────────── second (0-59)
│ ┌───────────── minute (0-59)
│ │ ┌───────────── hour (0-23)
│ │ │ ┌───────────── day of month (1-31)
│ │ │ │ ┌───────────── month (1-12)
│ │ │ │ │ ┌───────────── day of week (0-7)
│ │ │ │ │ │
* * * * * *

# Every 30 seconds
*/30 * * * * *

# At second 0 of every minute (same as 5-field)
0 * * * * *

Cron in Different Systems

Linux Crontab

# Edit your crontab
crontab -e

# List your cron jobs
crontab -l

# Example entry with output logging
0 2 * * * /home/user/backup.sh >> /var/log/backup.log 2>&1

# Example with PATH set
PATH=/usr/local/bin:/usr/bin:/bin
0 * * * * python3 /home/user/script.py

GitHub Actions

on:
  schedule:
    # Runs at 00:00 UTC every day
    - cron: '0 0 * * *'

    # Runs every Monday at 9 AM UTC
    - cron: '0 9 * * 1'

Kubernetes CronJob

apiVersion: batch/v1
kind: CronJob
metadata:
  name: daily-cleanup
spec:
  schedule: "0 3 * * *"  # 3 AM daily
  jobTemplate:
    spec:
      template:
        spec:
          containers:
          - name: cleanup
            image: busybox
            command: ["/bin/sh", "-c", "echo Cleaning up"]
          restartPolicy: OnFailure

Node.js (node-cron)

const cron = require('node-cron');

// Run every day at midnight
cron.schedule('0 0 * * *', () => {
  console.log('Running daily task');
});

// Run every 5 minutes
cron.schedule('*/5 * * * *', () => {
  console.log('Running every 5 minutes');
});

Common Pitfalls

• Time zones matter — Linux cron uses the system timezone. GitHub Actions uses UTC. Kubernetes uses UTC. AWS uses UTC. Always check which timezone your cron system uses.
• Day-of-month and day-of-week combine with OR — 0 0 15 * 5 runs on the 15th and every Friday, not "the 15th if it's a Friday."
• Environment is minimal — cron jobs run with a limited PATH. Always use full paths to executables or set PATH explicitly.
• No output by default — redirect stdout/stderr to a log file or /dev/null to avoid cron sending emails.
• Overlapping runs — if a job takes longer than the interval, you'll have multiple instances running. Use flock for locking.

Predefined Shortcuts

Many cron implementations support these shortcuts:

Shortcut	Equivalent	Description
@yearly	0 0 1 1 *	Once a year (Jan 1st, midnight)
@monthly	0 0 1 * *	Once a month (1st, midnight)
@weekly	0 0 * * 0	Once a week (Sunday, midnight)
@daily	0 0 * * *	Once a day (midnight)
@hourly	0 * * * *	Once an hour (minute 0)
@reboot	—	Run once at system startup

The syntax of cron expressions shares some concepts with regular expressions — both use special characters to define patterns. The * wildcard and range syntax (1-5) work similarly in both contexts.

Building cron expressions by hand is error-prone. Use our Cron Expression Generator to visually build and validate cron schedules — see exactly when your job will run next without guessing. Need to convert between cron timestamps and human dates? Our Epoch Converter can help.