Cron Syntax Reference | The Garnet Wiki

Cron syntax defines when and how often a command or script runs on Unix-like systems. Use this reference when writing, debugging, or maintaining crontab entries—especially when jobs fail silently at 2:17 AM on a Tuesday, or when a daily backup misses a day due to a typo in the minute field.

Basic Cron Syntax

A cron entry consists of six fields: minute hour day-of-month month day-of-week command Each field uses a specific format, and all fields are space-separated.

# Example: Run backup at 2:17 AM every day
17 2 * * * /usr/local/bin/backup.sh

minute: 0–59
hour: 0–23 (0 = midnight)
day-of-month: 1–31
month: 1–12 (1 = January) or names (e.g., Jan, Apr)
day-of-week: 0–7 (both 0 and 7 = Sunday) or names (e.g., Mon, Fri)
command: any shell command, including arguments and pipes.

Run a Job at a Specific Time

Use fixed values in each field to schedule a job at an exact time.

# Run every Monday at 9:05 AM
05 9 * * 1 /usr/bin/notify-staff.sh

1 for Monday (0 = Sunday)
05 for 5 minutes past the hour
9 for 9 AM
* for every month, every day-of-month

Common pitfall: Confusing day-of-week 1 (Monday) with month 1 (January). Silent failure: Using 1 in month field but expecting January, when job runs on 1st of every month instead.

Run a Job Every N Units of Time

Use */N to run a job every N units.

# Every 15 minutes
*/15 * * * * /usr/local/bin/check-service.sh

*/15 in minute field: minutes 0, 15, 30, 45
* in hour, day-of-month, month, day-of-week

# Every 3 hours, starting at hour 0
0 */3 * * * /usr/local/bin/daily-report.sh

Runs at 00:00, 03:00, 06:00, ..., 21:00

Edge case: */1 is equivalent to *, but */1 is explicit and useful in documentation.

Run a Job on Specific Days or Months

Use lists of values, separated by commas.

# Run every first of the month and every 15th
0 0 1,15 * * /usr/local/bin/monthly-accounts.sh

Runs at midnight on the 1st and 15th of every month
0 0 = 12:00 AM

# Run on weekends and holidays (specific days)
0 8 * * 0,6 /usr/local/bin/weekend-report.sh

Runs at 8 AM on Sunday (0) and Saturday (6)

Confusion point: day-of-week uses 0 and 7 for Sunday. Best practice: Use 0,6 for weekends instead of 0,6,7. Silent failure: 0,6,7 in day-of-week implies Sunday + Saturday + Sunday again—overlapping days.

Use Ranges and Combinations

Combine ranges (N-M) with lists and step intervals.

# Run every weekday (Mon–Fri) at 9 AM and 4 PM
0 9,16 * * 1-5 /usr/local/bin/daily-work.sh

9 AM and 4 PM every Monday through Friday

# Run every 10 minutes during business hours: 8 AM to 6 PM, Mon–Fri
*/10 8-18 * * 1-5 /usr/local/bin/business-hour-monitor.sh

Minutes 0,10,20,...,50 every hour from 8 to 18 (6 PM)
Only on Mon–Fri

Edge case: 1-5 includes 1,2,3,4,5 — not 1,2,3,4,5,6 for Mon–Sat. Common mistake: Writing 1-6 for Mon–Sat, but expecting 1-5 for Mon–Fri.

Run Jobs on Specific Month Names and Day Names

Use names instead of numbers for month and day-of-week.

# Run every first of the month, every spring month
0 0 1 Mar,Jun,Sep,Dec * /usr/local/bin/quarterly-report.sh

Runs at midnight on the 1st of March, June, September, December

# Run every Friday at 2 PM in the winter months
0 14 * * Fri,Mon,Tue,Wed,Thu /usr/local/bin/winter-work.sh

Runs every weekday at 2 PM — but only in winter months (Nov, Dec, Jan, Feb, Mar)

Critical detail: Month names are case-insensitive. Silent failure: jan in month field matches January, but Jan also works. Best practice: Use full capitalized names (January, Saturday) for clarity in production crontabs.

Run a Job at a Specific Time in a Specific Month

Combine multiple conditions using lists and ranges.

# Run on the 1st and 15th of January, March, May, July, and September
0 0 1,15 Jan,Mar,May,Jul,Sep * /usr/local/bin/quarterly-billing.sh

Runs at midnight on the 1st and 15th of Jan, Mar, May, Jul, Sep
* in month means every month, but Jan,Mar,May,Jul,Sep restricts to those

Confusion: Jan,Mar,May,Jul,Sep in month field means “run every January, March, etc.” Edge case: 1,15 Jan,Mar means “1st and 15th of January and March only”.

Use Special Strings (Predefined Schedules)

Cron supports special strings in the first field (minute) to define common intervals.

# Run every minute
* * * * * /usr/local/bin/heartbeat-check.sh

# Run every hour
0 * * * * /usr/local/bin/hourly-maintenance.sh

# Run every day at midnight
0 0 * * * /usr/local/bin/daily-backup.sh

# Run every day at 1:00 AM
0 1 * * * /usr/local/bin/daily-sync.sh

# Run every week (Sundays at midnight)
0 0 * * 0 /usr/local/bin/weekly-report.sh

# Run every month (1st at midnight)
0 0 1 * * /usr/local/bin/monthly-summary.sh

# Run every year (1st January at midnight)
0 0 1 1 * /usr/local/bin/yearly-audit.sh

Key insight: * * * * * is the same as 0 * * * *, but * * * * * is more explicit for “every minute”.

Common error: Using 0 0 * * * for “daily” but forgetting that it runs every day at midnight, not every 24 hours. Sharp edge: 0 0 1 * * runs every month on the 1st, not every day at 1:00 AM.

Use Multiple Schedules in One Line

A single crontab entry can have multiple schedules by combining fields.

# Run at 2:17 AM every day, and 5:17 AM every weekday
17 2,5 * * 1-5 /usr/local/bin/daily-task.sh

Runs at 2:17 AM every day
Also runs at 5:17 AM every Monday–Friday

Powerful pattern: Use 17 2,5 * * 1-5 to run a job at multiple times on weekdays.

Edge case: 2,5 in hour means 2 AM and 5 AM, not 2 and 5 PM. Common mistake: Writing 2,5 but expecting 2 PM and 5 PM.

Run Jobs with Complex Expressions

Combine lists, ranges, step, and names in a single field.

# Run every 10 minutes during business hours, every weekday
*/10 8-18 * * 1-5 /usr/local/bin/business-hour-monitor.sh

Every 10 minutes from 8:00 AM to 6:00 PM, every Monday through Friday

# Run every 15 minutes, but only on 1st, 15th, and 25th of the month
*/15 * 1,15,25 * * /usr/local/bin/quarterly-check.sh

Runs at 15-minute intervals on the 1st, 15th, and 25th of every month

Critical detail: */15 in minute field means every 15 minutes — not 15 minutes past the hour.

Best practice: Use 0 0 * * 1-5 for “run every Monday through Friday at midnight” Silent failure: Using 0 0 * * 1-5 but expecting a job that runs at midnight every weekday, but the job runs at midnight every Monday through Friday, including weekends.

Advanced: Use `@` Predefined Schedules

The @ symbol simplifies common cron schedules.

# Run every 30 minutes
@every30min /usr/local/bin/monitoring-check.sh

# Run every 5 minutes
@every5min /usr/local/bin/health-check.sh

# Run every day at 8 AM
@daily /usr/local/bin/daily-report.sh

# Run every week on Monday at 8 AM
@weekly /usr/local/bin/weekly-reminder.sh

# Run every month on the 1st at 8 AM
@monthly /usr/local/bin/monthly-summary.sh

# Run every year on January 1st at 8 AM
@yearly /usr/local/bin/yearly-audit.sh

# Run every 10 minutes
@every10min /usr/local/bin/ten-minute-check.sh

Configuration: @everyNmin, @everyNhour, @everyNday, @everyNweek, @everyNmonth, @everyNyear.

Edge case: @every30min is equivalent to */30 * * * * Best practice: Use @daily instead of 0 0 * * * for clarity.

Silent failure: @weekly runs on Monday at midnight, but @weekly in crontab uses 0 0 * * 1 — not 0 0 1 * *. Sharp edge: @monthly uses 0 0 1 * *, but @monthly in crontab expects 0 0 1 * * — so @monthly is not 0 0 1 * * but 0 0 1 * * with a default 0 0 1 * *.

Common Failures and Debugging Tips

Job runs but nothing appears in logs:

Ensure the command includes absolute paths. backup.sh in crontab may fail if PATH is not set.

# Common crontab setup with PATH
PATH=/usr/local/bin:/usr/bin:/bin
SHELL=/bin/bash
[email protected]

# Job with relative paths
0 2 * * * backup.sh

Job runs but fails silently:

Redirect output and errors:

# Log all output and errors
0 2 * * * /usr/local/bin/backup.sh >> /var/log/backup.log 2>&1

Job runs every day but misses a day:

Check day-of-week and day-of-month for overlap. Use 0 0 * * * for daily, but ensure crontab is installed and cron is running.

Job runs at wrong time:

Check timezone: crontab runs in system timezone, not user’s timezone. Use TZ=America/New_York in crontab to set timezone.

# Set timezone for crontab
TZ=America/New_York
0 8 * * * /usr/local/bin/ny-report.sh

Job runs but script not found:

Use absolute paths. crontab does not inherit PATH from shell.

Multiple crontabs, but only one is active:

Check that cron is running: systemctl status cron Check logs: /var/log/cron or journalctl -u cron

Crontab not reloading after edits:

Use crontab -e and crontab -l to verify.

Summary of Key Rules

minute field: 0–59
hour field: 0–23
day-of-month: 1–31
month: 1–12 or name (Jan, Feb)
day-of-week: 0–7 (0 = Sunday, 7 = Sunday)
* means “every” in that field
*/N means “every N units”
N-M means “from N to M”
N,M,... means “list of values”
@ schedules: @hourly, @daily, @weekly, @monthly, @yearly, @everyNmin, etc.
Use absolute paths in command field
Redirect output and error with >> file 2>&1
Set PATH, SHELL, MAILTO, and TZ in crontab header

Use this reference to write, read, and debug cron jobs with confidence.

This page was rewritten on 10 October 2026. It replaced a templated version that was not specific to its own title. How these pages are written and checked. If anything here is wrong, tell us at [email protected] and we will correct it.