owasp-amass/amass · error

failed to open resolvers file

Error message

failed to open resolvers file: %w

What it means

loadResolversFromFile reads a text file of newline-separated resolver IPs and wraps any os.ReadFile failure with this message. It is thrown when the resolvers file cannot be opened/read (missing file, bad permissions, or a path error). The underlying OS error is preserved via %w so it can be inspected with errors.Is/As.

Solutions

1. Verify the resolvers file exists at the configured path (ls the path, check for typos)
2. Fix file permissions so the process user can read it (chmod/chown)
3. If the path is relative, confirm the working directory or switch to an absolute path
4. Inspect the wrapped %w error (os.IsNotExist vs permission) to confirm which OS-level cause applies

Example fix

// before
cfg.LoadResolversFromFile("/etc/amass/reslover.txt") // typo
// after
cfg.LoadResolversFromFile("/etc/amass/resolvers.txt")

if _, err := os.Stat(path); err != nil { return fmt.Errorf("resolvers file not accessible: %w", err) }

func fileReadable(path string) bool { f, err := os.Open(path); if err != nil { return false }; f.Close(); return true }

res, err := loadResolversFromFile(p)
if err != nil {
    var perr *fs.PathError
    if errors.As(err, &perr) && os.IsNotExist(perr) { /* fix path */ }
    return err
}

When it happens

Trigger: Config-loadResolversFromFile is called with a path that does not exist, points to a directory, or is unreadable (permission denied); loadResolverSettings passes the user-supplied resolvers file path from settings.

Common situations: Typo in the resolvers file path in the amass config; file deleted or moved after config was written; running in a container where the file was not mounted; insufficient read permissions on the file.

Understand the failure class

Background: "failed to read file", EACCES, ENOENT and "could not read <path>" errors: when a program can't read a file from disk — this error's family across 49 libraries.

Related errors

• failed to parse the file
• active enumeration cannot be performed without DNS…
• alterations enabled is not a bool
• alterations is not a map[string]interface
• alterations wordlist_file is not an array

AI-assisted analysis of owasp-amass/amass@79299dce87 (2026-09-06). Data as JSON: /api/errors/9de06604a70635c0. Report an issue: GitHub.

Appendix: source

Thrown at config/resolvers.go:226

	if len(resolverIPs) == 0 {
		return errors.New("no valid resolvers were found")
	}

	c.Resolvers = resolverIPs

	return nil
}

func (c *Config) loadResolversFromFile(path string) ([]string, error) {
	absPath, err := filepath.Abs(path)
	if err != nil {
		return nil, fmt.Errorf("failed to get absolute path: %v", err)
	}

	data, err := os.ReadFile(absPath)
	if err != nil {
		return nil, fmt.Errorf("failed to open resolvers file: %w", err)
	}

	// Split the file data by newlines to get the IP addresses.
	lines := strings.Split(string(data), "\n")

	var resolvers []string
	for _, line := range lines {
		line = strings.TrimSpace(line)
		// Skip empty lines.
		if line == "" {
			continue
		}

		// Check if each line in the file is a valid IP address.
		ip := net.ParseIP(line)
		if ip == nil {
			return nil, fmt.Errorf("invalid IP address in resolvers file: %s", line)
		}

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