kubernetes/kubernetes · error

unable to get hostname: %v

Error message

unable to get hostname: %v

What it means

In makeLeaderElectionConfig, the scheduler obtains the OS hostname via os.Hostname() to build a unique leader election identity (hostname + UUID). If the kernel returns an error from the hostname syscall, the function wraps it with this message and returns.

Source

Thrown at cmd/kube-scheduler/app/options/options.go:356

		}
	}

	c.Client = client
	c.InformerFactory = scheduler.NewInformerFactory(client, 0, o.InformerName)
	dynClient := dynamic.NewForConfigOrDie(c.KubeConfig)
	c.DynInformerFactory = dynamicinformer.NewFilteredDynamicSharedInformerFactory(dynClient, 0, corev1.NamespaceAll, nil)
	c.LeaderElection = leaderElectionConfig
	c.ComponentGlobalsRegistry = o.ComponentGlobalsRegistry

	return c, nil
}

// makeLeaderElectionConfig builds a leader election configuration. It will
// create a new resource lock associated with the configuration.
func makeLeaderElectionConfig(config componentbaseconfig.LeaderElectionConfiguration, kubeConfig *restclient.Config, recorder record.EventRecorder) (*leaderelection.LeaderElectionConfig, error) {
	hostname, err := os.Hostname()
	if err != nil {
		return nil, fmt.Errorf("unable to get hostname: %v", err)
	}
	// add a uniquifier so that two processes on the same host don't accidentally both become active
	id := hostname + "_" + string(uuid.NewUUID())

	rl, err := resourcelock.NewFromKubeconfig(config.ResourceLock,
		config.ResourceNamespace,
		config.ResourceName,
		resourcelock.ResourceLockConfig{
			Identity:      id,
			EventRecorder: recorder,
		},
		kubeConfig,
		config.RenewDeadline.Duration)
	if err != nil {
		return nil, fmt.Errorf("couldn't create resource lock: %v", err)
	}

	return &leaderelection.LeaderElectionConfig{

View on GitHub (pinned to b882c60b40)

Solutions

1. Set a hostname explicitly on the node/container: `hostnamectl set-hostname <name>` or set the `HOSTNAME` env / `--hostname-override` in the container runtime.
2. Relax the seccomp/security profile to allow hostname syscalls.
3. Investigate the underlying os.Hostname() error to determine if it is a filesystem, kernel, or policy issue.

Example fix

// before — os.Hostname() fails in restricted container
hostname, err := os.Hostname()
if err != nil {
    return nil, fmt.Errorf("unable to get hostname: %v", err)
}

// after — allow override from env for restricted environments
hostname := os.Getenv("HOSTNAME")
if hostname == "" {
    hostname, err = os.Hostname()
    if err != nil {
        return nil, fmt.Errorf("unable to get hostname: %v", err)
    }
}

// Pre-check hostname availability
func validateHostname() error {
    _, err := os.Hostname()
    if err != nil {
        // Try env fallback
        if os.Getenv("HOSTNAME") == "" {
            return fmt.Errorf("hostname unavailable and HOSTNAME env not set: %w", err)
        }
    }
    return nil
}

hostname, err := os.Hostname()
if err != nil {
    // Fallback: use env var or node name from kubelet
    hostname = os.Getenv("HOSTNAME")
    if hostname == "" {
        return nil, fmt.Errorf("unable to get hostname: %v", err)
    }
    klog.Warningf("os.Hostname() failed, using HOSTNAME env: %s", hostname)
}

When it happens

Trigger: Calling makeLeaderElectionConfig when the OS hostname is unreadable. os.Hostname() can fail on systems where the hostname is not set, the node is in an invalid state, or the syscall is denied by a security policy (e.g., seccomp).

Common situations: Container with a restricted seccomp profile that blocks the uname/gethostname syscall, a broken /proc or hostname configuration, or a node that has not yet been assigned a hostname during early boot.

Related errors

• couldn't create resource lock: %v
• couldn't create leader elector: %v
• lost lease
• finished without leader elect
• CrashLoopBackOff

AI-assisted analysis of kubernetes/kubernetes@b882c60b40 (2026-08-07). Data as JSON: /api/errors/aabaafe67e509f96. Report an issue: GitHub.