Field-by-Field Breakdown of `*/15 * * * *`
| Position | Field Name | Allowed Values | Value in `*/15 * * * *` | Evaluation Meaning |
|---|---|---|---|---|
| 1 | Minute | 0 – 59 | */15 | */15 (At minutes 0, 15, 30, and 45) |
| 2 | Hour | 0 – 23 | * | * (Every hour: 0-23) |
| 3 | Day of Month | 1 – 31 | * | * (Every day of the month: 1-31) |
| 4 | Month | 1 – 12 | * | * (Every month: 1-12) |
| 5 | Day of Week | 0 – 6 (Sun-Sat) | * | * (Every day of the week: 0-6) |
The Standard Quarter-Hour Server Cadence
A 15-minute schedule is one of the most widely adopted enterprise intervals. Dividing the 60-minute hour into four clean quarters (:00, :15, :30, :45), it is the industry standard for SSL certificate monitoring, CDN invalidation batches, and RSS feed ingestion.
The step expression `*/15` evaluates to the set `[0, 15, 30, 45]`. Because 60 is evenly divisible by 15, execution intervals remain perfectly uniform across the transition from one hour to the next.
For teams running multiple 15-minute jobs on the same server, offsetting the minute field prevents CPU spikes. For instance, run Job A at `0,15,30,45 * * * *`, Job B at `5,20,35,50 * * * *`, and Job C at `10,25,40,55 * * * *`.
Common Production Scenarios for `*/15 * * * *`
RSS Feed & Content Syndication Ingestion
Fetches external RSS and Atom feeds for news aggregator websites without triggering DDoS protection on source publishers.
/usr/bin/node /opt/syndicator/fetch-feeds.jsGit Repository Auto-Sync & CI Mirroring
Pulls updates from origin git repositories and verifies working directory integrity on automated staging mirrors.
cd /var/www/site && git pull origin main --quietCloud Backup Verification & Heartbeat
Verifies that continuous database replication lag is under 900 seconds and alerts operations if replication freezes.
/usr/local/bin/check-repl-lag.shProduction Gotchas When Running `*/15 * * * *`
- Even Quarter-Hour Stampedes: Avoid stacking all your 15-minute scripts at minute :00 and :30. Stagger secondary jobs to :05 or :10.
- Timezone adjustments: Daylight saving time shifts can cause a duplicate or skipped run during clock changes if relying on local time. Run servers on UTC.
- Script Permissions: Always ensure the target executable has `chmod +x` permissions and is owned by the user running the crontab.
Frequently Asked Questions About `*/15 * * * *`
Does `*/15 * * * *` execute at minute 45?
Yes. The four execution points in every hour are minute 0, minute 15, minute 30, and minute 45.
How do I offset a 15-minute job by 5 minutes?
Use an explicit list: `5,20,35,50 * * * * /path/to/script.sh`. This maintains a 15-minute interval while running at non-standard minutes.
What happens if my 15-minute script hangs indefinitely?
By default, cron does not enforce timeouts. A hung script will remain active until killed. Use the `timeout` command to protect it: `*/15 * * * * /usr/bin/timeout 600 /path/to/script.sh`.