What causes "failed to access wifi data: %w" in prometheus/node_exporter?

Confirm the host actually has wireless interfaces and cfg80211/nl80211 support (lsmod | grep cfg80211).

failed to access wifi data

Error message

failed to access wifi data: %w

What it means

The wifi collector's Update creates a wifi stat handle via the local wifi library (netlink-based). Errors from establishing that handle — other than os.ErrPermission, which is downgraded to ErrNoData — are wrapped as 'failed to access wifi data: %w'. It means the collector could not begin querying wireless interface information at all.

Solutions

Confirm the host actually has wireless interfaces and cfg80211/nl80211 support (lsmod | grep cfg80211).
Disable the wifi collector on hosts with no wireless hardware.
Run in the host network namespace so netlink queries reach the real kernel.
Check the wrapped error; EPERM is intentionally downgraded to ErrNoData.

Defensive patterns

Strategy: try-catch

Validate before calling

// probe nl80211 availability before enabling wifi collection
// e.g. run: iw list  (or check /sys/class/net/*/wireless exists)
hasWireless := false
ents, _ := os.ReadDir("/sys/class/net")
for _, e := range ents {
    if _, err := os.Stat("/sys/class/net/" + e.Name() + "/wireless"); err == nil {
        hasWireless = true
    }
}
_ = hasWireless

Try / catch

if err := c.Update(ch); err != nil {
    if errors.Is(err, ErrNoData) { return }
    if strings.Contains(err.Error(), "failed to access wifi data") {
        logger.Warn("wifi metrics unavailable", "err", err)
        return
    }
    return err
}

Prevention

Only enable the wifi collector on hosts with actual wireless interfaces.
Run with the host network namespace so netlink/nl80211 queries succeed.
Verify cfg80211/nl80211 kernel support before deployment.
Treat EPERM-derived ErrNoData as an expected skip, not a failure.

When it happens

Trigger: wifiCollector.Update when the wifi stat handle creation fails with non-EPERM errors — typically nl80211/cfg80211 not available in the kernel, or netlink socket creation failing.

Common situations: Running on servers/wired-only hosts without wireless extensions, kernels built without cfg80211/nl80211, containers without access to the host's network netlink namespace, and unprivileged users hitting permission-related paths (those return ErrNoData instead).

Related errors

AI-assisted analysis of prometheus/node_exporter@17ddd77c59 (2026-09-07). Data as JSON: /api/errors/3b2c4d3734b6fc18. Report an issue: GitHub.

Appendix: source

Thrown at collector/wifi_linux.go:166

	return &wifiCollector{
		logger: logger,
	}, nil
}

func (c *wifiCollector) Update(ch chan<- prometheus.Metric) error {
	stat, err := newWifiStater(*collectorWifi)
	if err != nil {
		// Cannot access wifi metrics, report no error.
		if errors.Is(err, os.ErrNotExist) {
			c.logger.Debug("wifi collector metrics are not available for this system")
			return ErrNoData
		}
		if errors.Is(err, os.ErrPermission) {
			c.logger.Debug("wifi collector got permission denied when accessing metrics")
			return ErrNoData
		}

		return fmt.Errorf("failed to access wifi data: %w", err)
	}
	defer stat.Close()

	ifis, err := stat.Interfaces()
	if err != nil {
		return fmt.Errorf("failed to retrieve wifi interfaces: %w", err)
	}

	for _, ifi := range ifis {
		// Some virtual devices have no "name" and should be skipped.
		if ifi.Name == "" {
			continue
		}

		c.logger.Debug("probing wifi device with type", "wifi", ifi.Name, "type", ifi.Type)

		ch <- prometheus.MustNewConstMetric(
			wifiInterfaceFrequencyHertz,

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