Quartz vs Unix cron.

The 30-second overview

Quartz is a Java-world scheduling library used inside Spring, JBoss, and various enterprise frameworks. Unix cron is the OS-level scheduler on Linux/macOS/BSD. They share a syntactic ancestor — Vixie cron from 1987 — but Quartz added features for finer scheduling.

Field count: 5 vs 6/7

Unix cron — 5 fields

┌────────── minute (0-59)
│ ┌──────── hour (0-23)
│ │ ┌────── day of month (1-31)
│ │ │ ┌──── month (1-12)
│ │ │ │ ┌── day of week (0-6, Sun=0)
* * * * *

Reading "minute hour day-of-month month day-of-week" left-to-right.

Quartz — 6 or 7 fields

┌───────────── second (0-59)
│ ┌─────────── minute (0-59)
│ │ ┌───────── hour (0-23)
│ │ │ ┌─────── day of month (1-31)
│ │ │ │ ┌───── month (1-12)
│ │ │ │ │ ┌─── day of week (1-7, Sun=1)
│ │ │ │ │ │ ┌─ year (optional, 1970-2099)
* * * * * *  *

Quartz adds a seconds field on the left and an optional year on the right. The day-of-week numbering is offset by one (Quartz: 1=Sunday; Unix: 0=Sunday).

Special characters Quartz adds

? — No specific value

Used in day-of-month or day-of-week fields to mean "no value here, use the other day field." In Quartz, you can't set both day fields meaningfully — one must be ?:

0 0 9 ? * MON-FRI    # Every weekday at 9 AM (Quartz)
0 0 9 15 * ?         # Every 15th of the month at 9 AM (Quartz)

L — Last

In day-of-month: the last day of the month (whether 28, 29, 30, or 31).
In day-of-week: the last weekday of the month (Saturday by default; 6L = last Friday).

0 0 0 L * ?          # Midnight on the last day of every month
0 0 0 ? * 6L         # Midnight on the last Friday of every month

W — Nearest weekday

In day-of-month: the weekday nearest to the given date. If the date falls on a weekend, fires on the closest weekday instead.

0 0 9 15W * ?        # At 9 AM on the weekday closest to the 15th
                     # (if 15th is Sat, fires Fri 14th; if Sun, fires Mon 16th)

# — Nth weekday of the month

Used in day-of-week. Format: dayOfWeek#n where n is which occurrence.

0 0 9 ? * 2#1        # 9 AM on the first Monday of every month
0 0 14 ? * 6#3       # 2 PM on the third Friday of every month

(In Quartz, Monday=2, since Sunday=1.)

The day-field interaction

This is the single biggest difference in behavior.

Unix cron: OR semantics

When both day-of-month and day-of-week are restricted (neither is *), Unix cron fires when EITHER matches. Example:

0 0 15 * 1   # Midnight on the 15th, AND midnight on every Monday

This is rarely what users want. To get "midnight on the 15th, only if it's a Monday," you have to gate inside your script.

Quartz: exactly one of the two must be ?

Quartz refuses to interpret two restricted day fields. You're forced to pick one as the "active" day field and mark the other ?:

0 0 0 15 * ?         # OK: Midnight on the 15th (ignore day-of-week)
0 0 0 ? * MON        # OK: Midnight every Monday (ignore day-of-month)
0 0 0 15 * MON       # ERROR: ambiguous
0 0 0 * * *          # ERROR: at least one day field must be ?

This is annoying for new users but eliminates the OR-vs-AND confusion entirely.

Migrating expressions

Unix → Quartz

Add a leading 0 for seconds, replace one day field with ?, and (if day-of-week is set) shift the numbers up by 1.

Quartz → Unix

Drop the seconds field, replace ? with *, shift day-of-week down by 1.

If the Quartz expression uses L, W, or #, there's no exact Unix equivalent. Workarounds:

• L (last day of month): use 28-31 in day-of-month, then check [[ $(date -d tomorrow +\%d) == 01 ]] in your script
• 15W: use 14,15,16 in day-of-month and gate on weekday inside the script
• 2#1 (first Monday): use 1-7 in day-of-month and 1 in day-of-week

Which should you use?

It usually isn't your choice — the framework picks for you:

When you have a choice (e.g., a Java application that could use either), prefer Quartz — the explicit ? requirement saves the OR-vs-AND confusion that bites everyone using Unix cron.

Written by Murugan Vellaichamy, software engineer. Suggestions or corrections? Contact us.