kubernetes/kops · error

reading %s: %w

Error message

reading %s: %w

What it means

findPhysicalInterfaceByMAC lists /sys/class/net via os.ReadDir to map the primary ENI's MAC to an interface name; this error means the directory itself could not be read, so no interface scan is possible. It is only reachable on a system whose /sys/class/net is missing or unreadable, which should not happen on a healthy Linux node.

Source

Thrown at nodeup/pkg/model/networking/eni_networking.go:215

	}
	defer resp.Content.Close()
	mac, err := io.ReadAll(resp.Content)
	if err != nil {
		return "", fmt.Errorf("reading primary MAC address from ec2 metadata: %w", err)
	}

	return findPhysicalInterfaceByMAC("/sys/class/net", strings.TrimSpace(string(mac)))
}

// findPhysicalInterfaceByMAC gives the name of the physical network interface that has the
// specified MAC address. The function ignores the virtual interfaces (veths, bridges, VLANs),
// because a virtual interface can have the same MAC address as a physical interface. The
// function gives an error if it does not find exactly one physical interface with this MAC
// address.
func findPhysicalInterfaceByMAC(sysClassNet string, mac string) (string, error) {
	entries, err := os.ReadDir(sysClassNet)
	if err != nil {
		return "", fmt.Errorf("reading %s: %w", sysClassNet, err)
	}

	var matches []string
	for _, entry := range entries {
		name := entry.Name()
		// The scan uses the "device" symlink in sysfs to know if an interface is physical.
		if _, err := os.Stat(filepath.Join(sysClassNet, name, "device")); err != nil {
			continue
		}
		address, err := os.ReadFile(filepath.Join(sysClassNet, name, "address"))
		if err != nil {
			continue
		}
		if strings.EqualFold(strings.TrimSpace(string(address)), mac) {
			matches = append(matches, name)
		}
	}

View on GitHub (pinned to 4c8573c808)

Solutions

1. Ensure nodeup runs on the host (or with /sys mounted) — check the sysfs mount: mount | grep sysfs
2. If in a container, run privileged or bind-mount /sys
3. Fix underlying filesystem issues if /sys is corrupted (usually requires reboot)
4. In tests, pass a valid fixture directory as sysClassNet

Example fix

// before: container without sysfs
docker run nodeup...
// after
docker run -v /sys:/sys:ro --privileged nodeup...

When it happens

Trigger: os.ReadDir("/sys/class/net") fails — sysfs not mounted, running in a restricted container/namespace where /sys is not available, or filesystem corruption.

Common situations: nodeup run inside a container lacking /sys mount (not on a real EC2 host); chroot/provisioning environments without sysfs; unit tests passing an invalid sysClassNet path.

Related errors

• no physical network interface found with MAC address %q
• error querying kubernetes version: %v
• error loading channel %q: %v
• error querying ec2 metadata service (for region): %v
• listing nodes in cluster: %v

AI-assisted analysis of kubernetes/kops@4c8573c808 (2026-09-05). Data as JSON: /api/errors/eb18770c7463caac. Report an issue: GitHub.