hashicorp/nomad · error

Failed to open current namespace: %v

Error message

Failed to open current namespace: %v

What it means

netNS.Do() first saves a handle to the caller's current network namespace via GetCurrentNS() so it can be restored after running the callback in the target namespace. This error wraps a failure to open that initial handle, aborting the entire Do() operation.

Source

Thrown at client/lib/nsutil/ns_linux.go:207

		}
		defer func() {
			err := threadNS.Set() // switch back
			if err == nil {
				// Unlock the current thread only when we successfully switched back
				// to the original namespace; otherwise leave the thread locked which
				// will force the runtime to scrap the current thread, that is maybe
				// not as optimal but at least always safe to do.
				runtime.UnlockOSThread()
			}
		}()

		return toRun(hostNS)
	}

	// save a handle to current network namespace
	hostNS, err := GetCurrentNS()
	if err != nil {
		return fmt.Errorf("Failed to open current namespace: %v", err)
	}
	defer hostNS.Close()

	var wg sync.WaitGroup
	wg.Add(1)

	// Start the callback in a new green thread so that if we later fail
	// to switch the namespace back to the original one, we can safely
	// leave the thread locked to die without a risk of the current thread
	// left lingering with incorrect namespace.
	var innerError error
	go func() {
		defer wg.Done()
		runtime.LockOSThread()
		innerError = containedCall(hostNS)
	}()
	wg.Wait()

View on GitHub (pinned to 482b49bf1a)

Solutions

1. Ensure /proc is mounted and /proc/self/ns/net is readable by the process
2. Raise the fd soft limit (ulimit -n) if EMFILE
3. Run with privileges allowing namespace file access (CAP_SYS_ADMIN / DAC override as needed)
4. Check the wrapped GetCurrentNS error for the exact errno
5. Pre-open/validate the netns path before invoking Do()

Example fix

// before
hostNS, err := GetCurrentNS() // fails: no /proc
if err != nil {
    return fmt.Errorf("Failed to open current namespace: %v", err)
}
// after
if _, err := os.Stat("/proc/self/ns/net"); err != nil {
    return fmt.Errorf("/proc/self/ns/net unavailable (mount /proc): %w", err)
}
hostNS, err := GetCurrentNS()
if err != nil {
    return fmt.Errorf("Failed to open current namespace: %w", err)
}

func ensureCurrentNsReadable() error {
    f, err := os.Open("/proc/self/ns/net")
    if err != nil {
        return fmt.Errorf("cannot open current netns (mount /proc?): %w", err)
    }
    return f.Close()
}

if err := withNetworkIsolation(work); err != nil {
    if strings.Contains(err.Error(), "Failed to open current namespace") {
        return fmt.Errorf("netns isolation unavailable; check /proc and privileges: %w", err)
    }
    return err
}

When it happens

Trigger: Calling Do() (e.g. via withNetworkIsolation) when GetCurrentNS() fails: /proc/self/ns/net cannot be opened due to missing /proc, fd exhaustion, or insufficient permissions.

Common situations: Client running in a container without /proc mounted; process at its open-file limit; hardened environments where namespace files are unreadable; very early startup before /proc is available.

Related errors

• failed to get the current netns: %v
• failed to open current netns: %v
• mount --make-rshared %s failed: %q
• mount --rbind %s %s failed: %q
• error from unshare: %v

AI-assisted analysis of hashicorp/nomad@482b49bf1a (2026-09-04). Data as JSON: /api/errors/25e831d6a00e7442. Report an issue: GitHub.