Every 30 Seconds

Use in your stack

# Two entries, offset by half a minute. At 30s this is the one
# interval where the crontab workaround stays genuinely tidy.
* * * * * flock -n /tmp/heartbeat.lock /usr/local/bin/heartbeat.sh
* * * * * sleep 30; flock -n /tmp/heartbeat.lock /usr/local/bin/heartbeat.sh

# Or a systemd timer — /etc/systemd/system/heartbeat.timer
# AccuracySec is required; the 1min default would coalesce both
# firings into a single per-minute run.
#   [Timer]
#   OnCalendar=*-*-* *:*:00/30
#   AccuracySec=1s

{
  "schedule": {
    "cron": "0/30 * * * * ?",
    "timezone": "UTC"
  }
}

// 6-field: second minute hour day-of-month month day-of-week
@Scheduled(cron = "*/30 * * * * *")
public void everyThirtySeconds() {
    // ...
}

// Simpler for pure intervals:
@Scheduled(fixedRate = 30000) // milliseconds
public void everyThirtySecondsFixedRate() {
    // ...
}

Next runs

Pick a timezone to see when this expression fires next.

Variations

Common use cases

• Polling a queue or inbox twice a minute for lower latency than a 1-minute cron.
• Refreshing a cache or health status on a 30-second heartbeat.
• Emitting a keep-alive or liveness ping to a monitoring system.
• Flushing a metrics buffer downstream at a steady twice-per-minute rate.

Gotchas

• **Unix crontab cannot do this in one line.** The 5-field format has no seconds field; its minimum interval is one minute. Two entries — one plain, one offset with `sleep 30` — is the standard workaround, and at this interval it's the tidiest it ever gets. See the Linux tab above.
• **If you reach for a systemd timer, set `AccuracySec=1s`.** It defaults to **1 minute**, so `OnCalendar=*-*-* *:*:00/30` alone lets systemd coalesce both firings into one per minute. The unit looks right and runs half as often as intended — this is the most common reason a sub-minute timer quietly misbehaves.
• In Spring, `*/30 * * * * *` is the 6-field form (seconds first) — not Unix's `*/30 * * * *`, which means every 30 *minutes*.
• In Quartz, use `0/30 * * * * ?` — `0/30` in the seconds field means "from second 0, every 30 seconds" (so it fires at :00 and :30 of each minute), and `?` fills the unused day-of-week field.
• `@Scheduled(fixedRate = 30000)` (Spring) or `tokio::time::interval` (Rust) expresses the same interval without a cron parser and is often the simpler choice.
• If a run can take longer than 30 seconds, prefer `fixedDelay` or an in-flight guard so runs don't overlap.

Frequently asked questions