Cron Expression Guide: Syntax, Examples, and Common Mistakes

Overview

Cron expressions are used everywhere: Linux scheduled tasks, Spring Boot scheduling, cloud automation, and CI jobs. This guide explains the syntax and provides ready-to-use examples.

Cron Expression Structure

A standard Unix cron expression has five fields. Quartz, commonly used in Java applications, uses six or seven fields.

Unix Five-Field Format

minute  hour  day-of-month  month  day-of-week
  *      *         *          *         *

Quartz Six-Field Format

second  minute  hour  day-of-month  month  day-of-week
  *       *      *         *          *         *

Field Values

Field	Unix position	Quartz position	Allowed values
Second	—	1st	0–59
Minute	1st	2nd	0–59
Hour	2nd	3rd	0–23
Day of month	3rd	4th	1–31
Month	4th	5th	1–12 or JAN–DEC
Day of week	5th	6th	0–6 (0 = Sunday) or SUN–SAT

Special Characters

Character	Meaning	Example
`*`	Any value	`*` in minute means every minute
`,`	List of values	`1,15,30` means minutes 1, 15, and 30
`-`	Range	`9-17` means hours 9 through 17
`/`	Start and interval	`0/5` means every 5 units starting at 0
`?`	No specific value	Used in day-of-month or day-of-week
`L`	Last day	`L` in day-of-month means last day of month
`W`	Nearest weekday	`15W` means nearest weekday to the 15th
`#`	Nth weekday	`2#1` means first Monday of the month

? is only used in the day-of-month and day-of-week fields because these two fields can conflict. If one is specified, the other should usually be ?.

Common Quartz Examples

Schedule	Quartz expression
Every day at 10:15 AM	`0 15 10 ? * *`
Every day at 10:00, 14:00, and 16:00	`0 0 10,14,16 * * ?`
Every hour at minute 40 from 9 AM to 5 PM	`0 40 9-17 * * ?`
Every 30 minutes from 10 AM to 4 PM	`0 0/30 10-16 ? * 2`
15th day of every month at 10:15 AM	`0 15 10 15 * ?`
Last day of every month at 10:15 AM	`0 15 10 L * ?`
Every Wednesday in March at 2:00 PM and 2:30 PM	`0 0,30 14 ? 3 WED`

Common Unix Examples

Schedule	Unix expression
Every day at 9:30 AM	`30 9 * * *`
Every 5 minutes	`/5 * * *`
Every Monday at 8:00 AM	`0 8 * * 1`
First day of every month at midnight	`0 0 1 * *`

Linux Crontab Example

# Edit the current user's cron jobs
crontab -e

# Add a job: back up the database every day at 2:30 AM
30 2 * * * /home/user/backup.sh >> /var/log/backup.log 2>&1

# List current cron jobs
crontab -l

# Remove all cron jobs
crontab -r

Always redirect output to a log file. Otherwise, job output is lost and troubleshooting becomes difficult.

Common Mistakes

0 and 7 both mean Sunday in some systems, but behavior can vary. Use 0 for consistency.
Do not specify both day-of-month and day-of-week with fixed values. Use ? for one of them.
Quartz and Unix have different field counts. Spring Boot uses the six-field Quartz format by default, where the first field is seconds.
Cron does not use the same environment as your shell. Use absolute paths or set PATH inside crontab.