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NervesHub collects health metrics from your devices and surfaces them in the web UI and API so you can monitor fleet health at a glance. Rather than building your own telemetry pipeline, you get CPU usage, memory consumption, load averages, and application-specific metrics flowing into NervesHub automatically — alongside alarms that fire when something goes wrong.

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Extensions

Health data does not arrive on its own — it is delivered by extensions, optional capabilities a device negotiates with NervesHub when it connects. Each one is enabled per product, and a device only sends data for the extensions its product has turned on and its client library supports. Enable the ones you need under Settings → Extensions on the product, then confirm they are also enabled on the device itself — the device page shows which extensions the device actually negotiated.
Extensions are version-negotiated. A device advertises which versions of each extension it supports when it connects, and NervesHub picks a compatible one. An older client that does not know about an extension simply never receives its messages.

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Built-in Metrics

NervesHubLink reports the following system metrics automatically when the device is connected:
  • CPU usage — percentage of CPU time spent in user and kernel space, sampled periodically
  • Memory usage — total, used, and free memory in bytes, plus swap if present
  • System load averages — 1-minute, 5-minute, and 15-minute load averages, matching the output of uptime on Linux
These metrics appear as time-series charts on the Device Detail page in NervesCloud. You can zoom into any time range to correlate a spike with a rollout or an alarm.

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Custom Metrics

Beyond the built-in system metrics, your application can report its own metrics through NervesHubLink. This lets you track application-specific values — such as the number of active connections, sensor readings, queue depths, or any other runtime measurement your firmware produces. Custom metrics appear alongside the built-in metrics on the Device Detail page and are available through the NervesHub API, so you can pull them into external dashboards or alerting systems using the same interface.

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Alarms

NervesHub fires alarms when metric values exceed configured thresholds. Alarms can be configured at the product level (applying to all devices) or overridden at the individual device level. When an alarm fires:
  • It appears on the Device Detail page under the Alarms section
  • It increments the alarm count shown on the Fleet Dashboard
  • It is recorded with a timestamp in the device’s alarm history, so you can see when it started and when it cleared
Alarm history lets you reconstruct what happened on a device during an incident even after the condition has resolved.

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Viewing Health in the UI

Open any device in the NervesCloud UI and navigate to the Health tab on the Device Detail page. There you’ll find:
  • Live charts for each metric, updating as new data arrives from the device
  • Historical charts letting you scroll back through past metric values
  • The current alarm state and a full alarm history with timestamps
The Fleet Dashboard also shows an aggregate view of alarm counts across all devices in your product, so you can spot a widespread issue — such as a memory leak in a new firmware version — before it affects your entire fleet.

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Device Logs

NervesHub can stream and store logs from your devices, giving you visibility into what the device was doing at any point in time. Use the nh CLI to access logs directly from the terminal.
Logs require the logging extension to be enabled on the product and supported by the device’s client library.
Fetch recent logs from a device:
Stream logs live as they arrive (follow mode):
Filter to error-level logs from the past hour:

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Log Flags

Use the following flags to narrow the log output to exactly what you need:
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string
Filter by log level. Accepted values are debug, info, warning, and error. Only log entries at or above the specified level are returned.
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string
Full-text search within log message content. Returns only entries whose message body contains the search string.
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string
Return logs from this time onward. Accepts relative durations like 30m, 2h, 1d, or absolute timestamps in RFC 3339 format.
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string
Return logs up to this point in time. Accepts the same format as --since. Use together with --since to define a fixed time window.
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integer
Maximum number of log entries to return. Useful when you want a quick sample without paging through the full history.
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boolean
Stream logs in real time as the device emits them, similar to tail -f. Press Ctrl+C to stop streaming.
Use --output json with nh device logs to get structured log output suitable for feeding into a log aggregation pipeline:
You can pipe this into tools like jq, forward it to a log collector, or store it alongside incident reports for post-mortem analysis.