kubernetes/kops · error

error reading fstab: %w

Error message

error reading fstab: %w

What it means

After filtering swap lines, disableSwap calls scanner.Err() on the bufio.Scanner reading /etc/fstab; any scan failure (e.g. a line exceeding bufio.MaxScanTokenSize) is wrapped in this error. It indicates fstab could not be fully parsed, so nodeup refuses to rewrite it.

Source

Thrown at nodeup/pkg/model/linode.go:78

	fstabBytes, err := os.ReadFile(fstabPath)
	if err != nil {
		return fmt.Errorf("failed to read %s: %w", fstabPath, err)
	}

	// Filter out swap entries
	var filteredLines []string
	scanner := bufio.NewScanner(bytes.NewReader(fstabBytes))
	for scanner.Scan() {
		line := scanner.Text()
		// Keep lines that don't contain " swap " or "\tswap\t"
		if !strings.Contains(line, " swap ") && !strings.Contains(line, "\tswap\t") {
			filteredLines = append(filteredLines, line)
		} else {
			klog.V(2).Infof("Removing swap entry from fstab: %s", line)
		}
	}
	if err := scanner.Err(); err != nil {
		return fmt.Errorf("error reading fstab: %w", err)
	}

	// Write filtered fstab back
	filteredContent := strings.Join(filteredLines, "\n") + "\n"
	c.AddTask(&nodetasks.File{
		Path:     fstabPath,
		Contents: fi.NewStringResource(filteredContent),
		Type:     nodetasks.FileType_File,
		Mode:     s("0644"),
		// Execute swapoff after updating fstab
		OnChangeExecute: [][]string{{"swapoff", "-a"}},
	})

	return nil
}

View on GitHub (pinned to 4c8573c808)

Solutions

1. Inspect /etc/fstab for malformed or extremely long lines and fix or remove them
2. Check dmesg for root-disk I/O errors and repair/replace the volume
3. Note the scan error is rare — most real failures surface earlier as error 711 (failed to read /etc/fstab)

if f, err := os.Open("/etc/fstab"); err == nil {
    sc := bufio.NewScanner(f)
    for sc.Scan() {
        if len(sc.Bytes()) > bufio.MaxScanTokenSize/2 {
            return fmt.Errorf("fstab line suspiciously long; fix file before nodeup")
        }
    }
    if err := sc.Err(); err != nil {
        return fmt.Errorf("fstab not scannable: %w", err)
    }
}

scanner := bufio.NewScanner(bytes.NewReader(fstabBytes))
if err := scanner.Err(); err != nil {
    if errors.Is(err, bufio.ErrTooLong) {
        return fmt.Errorf("fstab line exceeds scanner buffer: %w", err)
    }
    return fmt.Errorf("error reading fstab: %w", err)
}

When it happens

Trigger: bufio.Scanner hits a read/token error while iterating /etc/fstab — practically, an fstab line longer than the default 64KB scanner buffer, or an underlying I/O error mid-read.

Common situations: Corrupted or machine-generated fstab with a pathological very long line; disk I/O errors on a failing root volume.

Related errors

• failed to read %s: %w
• error disabling swap: %v
• error building linode node identifier: %w
• building nodeConfig for instanceGroup: %w
• marshalling nodeupConfig: %w

AI-assisted analysis of kubernetes/kops@4c8573c808 (2026-09-05). Data as JSON: /api/errors/8e6dd997e1d4bdcb. Report an issue: GitHub.