What causes "failed to open config for writing: %s" in bcicen/ctop?

Fix file/directory permissions on the config path (chmod 0644 file, writable dir)

failed to open config for writing: %s

Error message

failed to open config for writing: %s

What it means

config.Write opens the config file with os.OpenFile(O_RDWR|O_CREATE, 0644) before encoding TOML. If the file cannot be opened, the error is wrapped with the path context as 'failed to open config for writing'.

Source

Thrown at config/file.go:103

	cfgdir := filepath.Dir(path)
	// create config dir if not exist
	if _, err := os.Stat(cfgdir); err != nil {
		err = os.MkdirAll(cfgdir, 0755)
		if err != nil {
			return path, fmt.Errorf("failed to create config dir [%s]: %s", cfgdir, err)
		}
	}

	// remove prior to writing new file
	if err := os.Remove(path); err != nil {
		if !os.IsNotExist(err) {
			return path, err
		}
	}

	file, err := os.OpenFile(path, os.O_RDWR|os.O_CREATE, 0644)
	if err != nil {
		return path, fmt.Errorf("failed to open config for writing: %s", err)
	}

	writer := toml.NewEncoder(file)
	err = writer.Encode(exportConfig())
	if err != nil {
		return path, fmt.Errorf("failed to write config: %s", err)
	}

	return path, nil
}

// determine config path from environment
func getConfigPath() (path string, err error) {
	homeDir, ok := os.LookupEnv("HOME")
	if !ok {
		return path, fmt.Errorf("$HOME not set")
	}

View on GitHub (pinned to 59f00dd6aa)

Solutions

Fix file/directory permissions on the config path (chmod 0644 file, writable dir)
Remove or rename an invalid file sitting at the config path
Run without sudo or chown the config back to the current user

Example fix

// before
-rw------- root root config.toml   # app runs as non-root
// after
chown $USER config.toml && chmod 0644 config.toml

Defensive patterns

Strategy: try-catch

Validate before calling

if fi, err := os.Stat(path); err == nil && fi.IsDir() { /* path invalid: it's a directory */ }
if fi, err := os.Stat(path); err == nil { f, e := os.OpenFile(path, os.O_WRONLY, 0644); if e != nil { /* fix perms */ } else { f.Close() } }

Try / catch

_, err := config.Write()
if err != nil && strings.HasPrefix(err.Error(), "failed to open config for writing") {
    // correct file ownership/permissions and retry
}

Prevention

Keep config file perms 0644 and owned by the running user
Never point the config path at a directory
Avoid running the app under sudo (creates root-owned files)

When it happens

Trigger: os.OpenFile fails: directory doesn't exist or isn't writable, path is a directory, or permission denied on an existing config file.

Common situations: Config file owned by another user (created under sudo); config path is a directory; stale permissions after switching users or running in a container as a different UID.

Related errors

AI-assisted analysis of bcicen/ctop@59f00dd6aa (2026-09-02). Data as JSON: /api/errors/e9b3e355a3144d00. Report an issue: GitHub.