wrtie config needs sudo usually

README.md

@@ -25,6 +25,7 @@ The program:
 - Checks `valid users` entries against local accounts.
 - Offers to create missing local accounts with `useradd -M -s /usr/sbin/nologin <user>`.
 - If user creation fails because admin rights are needed, explains the issue and offers to retry with `sudo`.
+- If saving the Samba config or its backup needs admin rights, explains the issue and offers to retry with `sudo`.
 - Writes a timestamped backup before saving changes.
 
 If you create a local account for a Samba-authenticated share, you may still need to add the Samba password separately:

app.go

@@ -238,12 +238,20 @@ func (a *App) deleteShare(doc *Document) error {
 
 func (a *App) writeConfig(doc *Document) error {
 	backup := fmt.Sprintf("%s.bak.%s", a.configPath, time.Now().UTC().Format("20060102T150405Z"))
+	serialized := doc.Serialize()
+
 	if err := copyFile(a.configPath, backup); err != nil {
-		return fmt.Errorf("create backup %s: %w", backup, err)
+		if shouldOfferPrivilegeRetry(err) {
+			return a.writeConfigWithPrivilegeRetry(serialized, backup)
+		}
+		return friendlyWriteError("create backup", backup, err)
 	}
 
-	if err := os.WriteFile(a.configPath, []byte(doc.Serialize()), 0o644); err != nil {
+	if err := os.WriteFile(a.configPath, []byte(serialized), 0o644); err != nil {
-		return fmt.Errorf("write config: %w", err)
+		if shouldOfferPrivilegeRetry(err) {
+			return a.writeConfigWithPrivilegeRetry(serialized, backup)
+		}
+		return friendlyWriteError("write config", a.configPath, err)
 	}
 
 	a.printf("Config written to %s\n", a.configPath)
@@ -357,7 +365,7 @@ func (a *App) createUser(name string) error {
 	args := []string{"-M", "-s", "/usr/sbin/nologin", name}
 	if err := a.runner.Run("useradd", args...); err == nil {
 		return nil
-	} else if shouldOfferSudoRetry(err) {
+	} else if shouldOfferPrivilegeRetry(err) {
 		a.println("")
 		a.println("Creating a Linux user usually needs administrator permission.")
 		a.println("I can try again using sudo so you can enter your admin password.")
@@ -468,7 +476,7 @@ func copyFile(src, dst string) error {
 	return os.WriteFile(dst, data, 0o644)
 }
 
-func shouldOfferSudoRetry(err error) bool {
+func shouldOfferPrivilegeRetry(err error) bool {
 	if os.Geteuid() == 0 {
 		return false
 	}
@@ -478,3 +486,65 @@ func shouldOfferSudoRetry(err error) bool {
 		strings.Contains(text, "operation not permitted") ||
 		strings.Contains(text, "exit status")
 }
+
+func (a *App) writeConfigWithPrivilegeRetry(serialized, backup string) error {
+	a.println("")
+	a.println("Saving Samba settings usually needs administrator permission.")
+	a.println("I can try again using sudo so you can enter your admin password.")
+	a.flush()
+
+	canUseSudo := false
+	if a.lookPath != nil {
+		_, sudoErr := a.lookPath("sudo")
+		canUseSudo = sudoErr == nil
+	}
+	if !canUseSudo {
+		return friendlyWriteError("save Samba settings", a.configPath, os.ErrPermission)
+	}
+
+	retry, err := a.confirm("Retry saving with sudo", true)
+	if err != nil {
+		return err
+	}
+	if !retry {
+		return friendlyWriteError("save Samba settings", a.configPath, os.ErrPermission)
+	}
+
+	tempPath, err := a.writeTempConfig(serialized)
+	if err != nil {
+		return fmt.Errorf("prepare config for sudo save: %w", err)
+	}
+	defer os.Remove(tempPath)
+
+	if err := a.runner.Run("sudo", "cp", a.configPath, backup); err != nil {
+		return friendlyWriteError("create backup", backup, err)
+	}
+
+	if err := a.runner.Run("sudo", "install", "-m", "644", tempPath, a.configPath); err != nil {
+		return friendlyWriteError("write config", a.configPath, err)
+	}
+
+	a.printf("Config written to %s\n", a.configPath)
+	a.printf("Backup saved to %s\n", backup)
+	return nil
+}
+
+func (a *App) writeTempConfig(serialized string) (string, error) {
+	file, err := os.CreateTemp("", "samba-configer-*.conf")
+	if err != nil {
+		return "", err
+	}
+	defer file.Close()
+
+	if _, err := file.WriteString(serialized); err != nil {
+		return "", err
+	}
+	return file.Name(), nil
+}
+
+func friendlyWriteError(action, path string, err error) error {
+	if errors.Is(err, os.ErrPermission) || strings.Contains(strings.ToLower(err.Error()), "permission denied") {
+		return fmt.Errorf("%s %s: administrator permission is needed", action, path)
+	}
+	return fmt.Errorf("%s %s: %w", action, path, err)
+}