hashicorp/nomad · error

Error while detecting network interface %s during fingerprin

Error message

Error while detecting network interface %s during fingerprinting: %v

What it means

The network fingerprinter failed while trying to detect the network interface named in the client config (network_interface). It wraps the underlying detection error from findInterface. The fingerprinter returns this instead of a fingerprint result, so the client logs a fingerprint failure.

Source

Thrown at client/fingerprint/network.go:80

func (b *DefaultNetworkInterfaceDetector) Addrs(intf *net.Interface) ([]net.Addr, error) {
	return intf.Addrs()
}

// NewNetworkFingerprint returns a new NetworkFingerprinter with the given
// logger
func NewNetworkFingerprint(logger log.Logger) Fingerprint {
	f := &NetworkFingerprint{logger: logger.Named("network"), interfaceDetector: &DefaultNetworkInterfaceDetector{}}
	return f
}

func (f *NetworkFingerprint) Fingerprint(req *FingerprintRequest, resp *FingerprintResponse) error {
	cfg := req.Config

	// Find the named interface
	intf, err := f.findInterface(cfg.NetworkInterface)
	switch {
	case err != nil:
		return fmt.Errorf("Error while detecting network interface %s during fingerprinting: %v",
			cfg.NetworkInterface,
			err)
	case intf == nil:
		// No interface could be found
		return nil
	}

	// Create a sub-logger with common values to help with debugging
	logger := f.logger.With("interface", intf.Name)

	// Record the throughput of the interface
	var mbits int
	throughput := f.linkSpeed(intf.Name)
	if cfg.NetworkSpeed != 0 {
		mbits = cfg.NetworkSpeed
		logger.Debug("setting link speed to user configured speed", "mbits", mbits)
	} else if throughput != 0 {
		mbits = throughput

View on GitHub (pinned to 482b49bf1a)

Solutions

1. Verify cfg.NetworkInterface matches an interface shown by 'ip link' (or 'ifconfig').
2. Leave network_interface unset to auto-detect via the default route, or set it explicitly to a valid device.
3. Check the wrapped error (%v) for the root cause (no such interface, permission, no default route).
4. Confirm the interface exists at client startup; disable the network fingerprinter if not needed.

Example fix

// before (config)
network_interface = "etho"
// after
network_interface = "eth0"

intfName := cfg.NetworkInterface
if intfName != "" {
	if _, err := net.InterfaceByName(intfName); err != nil {
		return fmt.Errorf("configured network_interface %q does not exist: %w", intfName, err)
	}
}

if err := fp.Fingerprint(req); err != nil {
	if strings.Contains(err.Error(), "Error while detecting network interface") {
		log.Printf("network fingerprint failed: %v", err)
		return nil
	}
	return err
}

When it happens

Trigger: Client config sets a network_interface that findInterface cannot resolve, or the default-route lookup fails, causing findInterface to return an error which Fingerprint wraps in this message with the configured interface name.

Common situations: Typo or renamed interface in the Nomad client 'network_interface' config; interface removed after a network reconfiguration; container/VM without the expected interface; inability to determine the default route interface.

Related errors

• no CNI network config found
• failed to initialize network configurator: %v
• failed to configure networking for alloc: %v
• no network_interface given and failed to determine interface
• Client RPC advertise address is not advertisable: %v

AI-assisted analysis of hashicorp/nomad@482b49bf1a (2026-09-04). Data as JSON: /api/errors/3ac02a925a6b36b8. Report an issue: GitHub.