What causes "failed writing file %s: %v" in hyperledger/fabric?

Create the parent directory first (os.MkdirAll(filepath.Dir(file), 0o755)) before calling ToFile

failed writing file %s: %v

Error message

failed writing file %s: %v

What it means

ToFile serializes the Config struct to YAML and writes it to disk with os.WriteFile (mode 0600). This error wraps the os.WriteFile failure, meaning the YAML marshal succeeded but the file write itself failed. The library throws it so callers get a clear message identifying both the target path and the underlying OS error.

Source

Thrown at cmd/common/config.go:50

	if err := yaml.Unmarshal(configData, &config); err != nil {
		return Config{}, errors.Errorf("error unmarshalling YAML file %s: %s", file, err)
	}

	return config, validateConfig(config)
}

// ToFile writes the config into a file
func (c Config) ToFile(file string) error {
	if err := validateConfig(c); err != nil {
		return errors.Wrap(err, "config isn't valid")
	}
	b, err := yaml.Marshal(c)
	if err != nil {
		return errors.Wrap(err, "failed to marshal config")
	}
	if err := os.WriteFile(file, b, 0o600); err != nil {
		return errors.Errorf("failed writing file %s: %v", file, err)
	}
	return nil
}

func validateConfig(conf Config) error {
	nonEmptyElems := map[string]string{
		"MSPID":        conf.SignerConfig.MSPID,
		"IdentityPath": conf.SignerConfig.IdentityPath,
		"KeyPath":      conf.SignerConfig.KeyPath,
	}

	for key, value := range nonEmptyElems {
		if value == "" {
			return errors.Errorf("%s is mandatory and cannot be empty", key)
		}
	}

	return nil

View on GitHub (pinned to 2736b63f8f)

Solutions

Create the parent directory first (os.MkdirAll(filepath.Dir(file), 0o755)) before calling ToFile
Verify the process has write permission on the target path (check ownership, run as correct user)
Confirm the path is a file, not a directory, and the disk isn't full
Inspect the wrapped %v OS error for the exact errno

Example fix

// before
if err := conf.ToFile("/etc/fabric/config.yaml"); err != nil { ... }
// after
os.MkdirAll("/etc/fabric", 0o755)
if err := conf.ToFile("/etc/fabric/config.yaml"); err != nil { log.Fatal(err) }

Defensive patterns

Strategy: validation

Validate before calling

info, err := os.Stat(file)
if err != nil || info.IsDir() {
    return fmt.Errorf("cannot write config to %s", file)
}
if err := os.MkdirAll(filepath.Dir(file), 0o755); err != nil {
    return err
}

Type guard

func writablePath(p string) bool {
    info, err := os.Stat(filepath.Dir(p))
    return err == nil && info.IsDir()
}

Try / catch

if err := conf.ToFile(path); err != nil {
    var pe *os.PathError
    if errors.As(err, &pe) { log.Printf("write failed at %s: %v", pe.Path, pe.Err) }
}

Prevention

Always MkdirAll the parent directory before ToFile
Use mode 0600 paths under the current user's home or an explicitly writable dir
Check disk space in automation before persisting
Never pass a directory path as the target file

When it happens

Trigger: Calling Config.ToFile (directly or via persistConfig) when the target path is in a non-existent directory, the process lacks write permission, the path is a directory, or the disk is full.

Common situations: Persisting config to ~/.fabric/... before the directory exists; read-only filesystem or container volume; running as non-root user while writing to a root-owned path; typo'd or empty file path.

Understand the failure class

Background: "failed to write file", "Could not save figure", "Error saving remote file" — file write failed: causes and fixes across languages and libraries — this error's family across 38 libraries.

Related errors

AI-assisted analysis of hyperledger/fabric@2736b63f8f (2026-09-04). Data as JSON: /api/errors/f9b753ce4762b577. Report an issue: GitHub.