smarter client flow

app.go

@@ -45,6 +45,7 @@ func (OSCommandRunner) Run(name string, args ...string) error {
 
 type App struct {
 	configPath string
+	fstabPath  string
 	users      UserManager
 	runner     CommandRunner
 	lookPath   LookPathFunc
@@ -75,9 +76,22 @@ type CIFSMountConfig struct {
 	ReadOnly   bool
 }
 
+type FstabMountEntry struct {
+	LineIndex   int
+	Source      string
+	MountPoint  string
+	FSType      string
+	Options     []string
+	Dump        string
+	Pass        string
+	RawLine     string
+	DisplayName string
+}
+
 func NewApp(configPath string, users UserManager, runner CommandRunner, lookPath LookPathFunc) *App {
 	return &App{
 		configPath: configPath,
+		fstabPath:  "/etc/fstab",
 		users:      users,
 		runner:     runner,
 		lookPath:   lookPath,
@@ -206,63 +220,55 @@ loaded:
 }
 
 func (a *App) setupClientMount() error {
+	for {
+		entries, err := a.loadCIFSMountEntries()
+		if err != nil {
+			return err
+		}
+
 		a.println("")
 		a.println("Client mount setup")
 		a.println("==================")
-	a.println("This will help connect this computer to a shared folder on another server.")
+		a.println("This computer can connect to Samba or CIFS shares listed in /etc/fstab.")
+		a.println("Current client mounts:")
+		if len(entries) == 0 {
+			a.println("  (none)")
+		} else {
+			for i, entry := range entries {
+				a.printf("  %d. %s -> %s\n", i+1, entry.DisplayName, entry.MountPoint)
+			}
+		}
+		a.println("")
+		a.println("[a] add client mount")
+		a.println("[e] edit client mount")
+		a.println("[d] delete client mount")
+		a.println("[b] back")
 		a.flush()
 
-	if err := a.ensureCIFSUtilsInstalled(); err != nil {
+		choice, err := a.prompt("Select an action")
-		return err
-	}
-
-	cfg, err := a.collectCIFSMountConfig()
 		if err != nil {
 			return err
 		}
 
-	if err := a.ensureMountPoint(cfg.MountPoint); err != nil {
+		switch strings.ToLower(choice) {
+		case "a", "add":
+			if err := a.addClientMount(); err != nil {
 				return err
 			}
-
+		case "e", "edit":
-	line := buildFstabLine(cfg)
+			if err := a.editClientMount(entries); err != nil {
-	a.println("")
-	a.println("Suggested /etc/fstab line:")
-	a.println(line)
-	a.println("")
-	a.println("This will store the username and password directly in /etc/fstab.")
-	a.println("That is simple for home use, but less secure than a credentials file.")
-	a.flush()
-
-	addLine, err := a.confirm("Add this line to /etc/fstab now", true)
-	if err != nil {
 				return err
 			}
-	if !addLine {
+		case "d", "delete":
+			if err := a.deleteClientMount(entries); err != nil {
+				return err
+			}
+		case "b", "back":
 			return nil
+		default:
+			a.println("Unknown choice.")
 		}
-
-	if err := a.appendFstabLine(line); err != nil {
-		return err
 	}
-
-	a.println("")
-	a.println("The mount entry was added to /etc/fstab.")
-	mountNow, err := a.confirm("Try mounting it now", true)
-	if err != nil {
-		return err
-	}
-	if mountNow {
-		if err := a.reloadSystemdIfNeeded(); err != nil {
-			return err
-		}
-		if err := a.mountCIFS(cfg.MountPoint); err != nil {
-			return err
-		}
-		a.println("The network share was mounted.")
-	}
-
-	return nil
 }
 
 func (a *App) manageUsers(doc *Document) error {
@@ -638,53 +644,68 @@ func (a *App) ensureCIFSUtilsInstalled() error {
 	return nil
 }
 
-func (a *App) collectCIFSMountConfig() (CIFSMountConfig, error) {
+func (a *App) collectCIFSMountConfig(defaults CIFSMountConfig) (CIFSMountConfig, error) {
-	server, err := a.prompt("Server name or IP")
+	server, err := a.promptDefault("Server name or IP", defaults.Server)
 	if err != nil {
 		return CIFSMountConfig{}, err
 	}
-	share, err := a.prompt("Share name on that server")
+	share, err := a.promptDefault("Share name on that server", defaults.Share)
 	if err != nil {
 		return CIFSMountConfig{}, err
 	}
 	mountPointDefault := filepath.Join("/mnt", strings.TrimSpace(share))
+	if defaults.MountPoint != "" {
+		mountPointDefault = defaults.MountPoint
+	}
 	mountPoint, err := a.promptDefault("Local mount folder", mountPointDefault)
 	if err != nil {
 		return CIFSMountConfig{}, err
 	}
-	username, err := a.prompt("Username for the remote share")
+	username, err := a.promptDefault("Username for the remote share", defaults.Username)
 	if err != nil {
 		return CIFSMountConfig{}, err
 	}
-	password, err := a.prompt("Password for the remote share")
+	password, err := a.promptDefault("Password for the remote share", defaults.Password)
 	if err != nil {
 		return CIFSMountConfig{}, err
 	}
-	domain, err := a.promptDefault("Domain or workgroup (optional)", "")
+	domain, err := a.promptDefault("Domain or workgroup (optional)", defaults.Domain)
 	if err != nil {
 		return CIFSMountConfig{}, err
 	}
-	uid, err := a.promptDefault("Local owner username or uid (optional)", "")
+	uid, err := a.promptDefault("Local owner username or uid (optional)", defaults.UID)
 	if err != nil {
 		return CIFSMountConfig{}, err
 	}
-	gid, err := a.promptDefault("Local group name or gid (optional)", "")
+	gid, err := a.promptDefault("Local group name or gid (optional)", defaults.GID)
 	if err != nil {
 		return CIFSMountConfig{}, err
 	}
-	fileMode, err := a.promptDefault("File permissions", "0664")
+	fileModeDefault := defaults.FileMode
+	if fileModeDefault == "" {
+		fileModeDefault = "0664"
+	}
+	fileMode, err := a.promptDefault("File permissions", fileModeDefault)
 	if err != nil {
 		return CIFSMountConfig{}, err
 	}
-	dirMode, err := a.promptDefault("Folder permissions", "0775")
+	dirModeDefault := defaults.DirMode
+	if dirModeDefault == "" {
+		dirModeDefault = "0775"
+	}
+	dirMode, err := a.promptDefault("Folder permissions", dirModeDefault)
 	if err != nil {
 		return CIFSMountConfig{}, err
 	}
-	autoMount, err := a.confirm("Mount automatically at startup", true)
+	autoMountDefault := true
+	if defaults.Server != "" || defaults.Share != "" || defaults.MountPoint != "" {
+		autoMountDefault = defaults.AutoMount
+	}
+	autoMount, err := a.confirm("Mount automatically at startup", autoMountDefault)
 	if err != nil {
 		return CIFSMountConfig{}, err
 	}
-	readOnly, err := a.confirm("Make this mount read-only", false)
+	readOnly, err := a.confirm("Make this mount read-only", defaults.ReadOnly)
 	if err != nil {
 		return CIFSMountConfig{}, err
 	}
@@ -736,45 +757,6 @@ func (a *App) ensureMountPoint(path string) error {
 	return nil
 }
 
-func (a *App) appendFstabLine(line string) error {
-	content := line + "\n"
-	file, err := os.OpenFile("/etc/fstab", os.O_APPEND|os.O_WRONLY, 0)
-	if err == nil {
-		defer file.Close()
-		if _, err := file.WriteString(content); err == nil {
-			return nil
-		} else if !shouldOfferPrivilegeRetry(err) {
-			return fmt.Errorf("append mount entry to /etc/fstab: %w", err)
-		}
-	} else if !shouldOfferPrivilegeRetry(err) {
-		return fmt.Errorf("open /etc/fstab for update: %w", err)
-	}
-
-	a.println("")
-	a.println("Updating /etc/fstab needs administrator permission.")
-	a.println("I can try again using sudo so you can enter your admin password.")
-	a.flush()
-
-	retry, err := a.confirm("Retry updating /etc/fstab with sudo", true)
-	if err != nil {
-		return err
-	}
-	if !retry {
-		return errors.New("updating /etc/fstab was cancelled")
-	}
-
-	tempPath, err := a.writeTempConfig(content)
-	if err != nil {
-		return fmt.Errorf("prepare fstab update: %w", err)
-	}
-	defer os.Remove(tempPath)
-
-	if err := a.runner.Run("sudo", "sh", "-c", fmt.Sprintf("cat %s >> /etc/fstab", shellQuote(tempPath))); err != nil {
-		return fmt.Errorf("append mount entry to /etc/fstab with sudo: %w", err)
-	}
-	return nil
-}
-
 func (a *App) mountCIFS(path string) error {
 	if err := a.runPrivilegedOrLocal("mount", []string{path}, "Mounting the network share needs administrator permission."); err != nil {
 		return fmt.Errorf("mount %s: %w", path, err)
@@ -1432,6 +1414,414 @@ func shellQuote(value string) string {
 	return "'" + strings.ReplaceAll(value, "'", `'\''`) + "'"
 }
 
+func (a *App) loadCIFSMountEntries() ([]FstabMountEntry, error) {
+	data, err := os.ReadFile(a.fstabPath)
+	if err != nil {
+		return nil, fmt.Errorf("read %s: %w", a.fstabPath, err)
+	}
+	return parseCIFSMountEntries(string(data)), nil
+}
+
+func parseCIFSMountEntries(contents string) []FstabMountEntry {
+	lines := strings.Split(contents, "\n")
+	entries := make([]FstabMountEntry, 0)
+	for index, line := range lines {
+		entry, ok := parseFstabMountLine(line, index)
+		if ok {
+			entries = append(entries, entry)
+		}
+	}
+	return entries
+}
+
+func parseFstabMountLine(line string, index int) (FstabMountEntry, bool) {
+	trimmed := strings.TrimSpace(line)
+	if trimmed == "" || strings.HasPrefix(trimmed, "#") {
+		return FstabMountEntry{}, false
+	}
+
+	fields := strings.Fields(trimmed)
+	if len(fields) < 4 {
+		return FstabMountEntry{}, false
+	}
+
+	fsType := strings.ToLower(fields[2])
+	if fsType != "cifs" && fsType != "smbfs" {
+		return FstabMountEntry{}, false
+	}
+
+	entry := FstabMountEntry{
+		LineIndex:  index,
+		Source:     fields[0],
+		MountPoint: unescapeFstabValue(fields[1]),
+		FSType:     fields[2],
+		Options:    splitFstabOptions(fields[3]),
+		RawLine:    line,
+		DisplayName: fmt.Sprintf(
+			"%s (%s)",
+			unescapeFstabValue(fields[0]),
+			unescapeFstabValue(fields[2]),
+		),
+	}
+	if len(fields) > 4 {
+		entry.Dump = fields[4]
+	}
+	if len(fields) > 5 {
+		entry.Pass = fields[5]
+	}
+	if entry.Dump == "" {
+		entry.Dump = "0"
+	}
+	if entry.Pass == "" {
+		entry.Pass = "0"
+	}
+	if entry.DisplayName == " (cifs)" || entry.DisplayName == " (smbfs)" {
+		entry.DisplayName = entry.MountPoint
+	}
+	return entry, true
+}
+
+func splitFstabOptions(value string) []string {
+	if value == "" {
+		return nil
+	}
+
+	var options []string
+	var current strings.Builder
+	escaped := false
+	for _, r := range value {
+		switch {
+		case escaped:
+			current.WriteRune(r)
+			escaped = false
+		case r == '\\':
+			current.WriteRune(r)
+			escaped = true
+		case r == ',':
+			options = append(options, current.String())
+			current.Reset()
+		default:
+			current.WriteRune(r)
+		}
+	}
+	options = append(options, current.String())
+	return options
+}
+
+func unescapeFstabValue(value string) string {
+	value = strings.ReplaceAll(value, `\040`, " ")
+	value = strings.ReplaceAll(value, `\,`, ",")
+	value = strings.ReplaceAll(value, `\\`, `\`)
+	return value
+}
+
+func (a *App) addClientMount() error {
+	if err := a.ensureCIFSUtilsInstalled(); err != nil {
+		return err
+	}
+
+	cfg, err := a.collectCIFSMountConfig(CIFSMountConfig{})
+	if err != nil {
+		return err
+	}
+
+	if err := a.ensureMountPoint(cfg.MountPoint); err != nil {
+		return err
+	}
+
+	line := buildFstabLine(cfg)
+	if err := a.confirmAndWriteClientMount(line, -1, "Add this line to /etc/fstab now"); err != nil {
+		return err
+	}
+
+	a.println("")
+	a.println("The mount entry was added to /etc/fstab.")
+	return a.offerMountNow(cfg)
+}
+
+func (a *App) editClientMount(entries []FstabMountEntry) error {
+	entry, err := a.selectCIFSMount(entries)
+	if err != nil || entry == nil {
+		return err
+	}
+
+	cfg, ok := cifsMountConfigFromEntry(*entry)
+	if !ok {
+		return fmt.Errorf("could not read mount details from %s", entry.RawLine)
+	}
+
+	if err := a.ensureCIFSUtilsInstalled(); err != nil {
+		return err
+	}
+
+	updated, err := a.collectCIFSMountConfig(cfg)
+	if err != nil {
+		return err
+	}
+	if err := a.ensureMountPoint(updated.MountPoint); err != nil {
+		return err
+	}
+
+	line := buildFstabLine(updated)
+	if err := a.confirmAndWriteClientMount(line, entry.LineIndex, "Save these changes to /etc/fstab now"); err != nil {
+		return err
+	}
+
+	a.println("")
+	a.println("The mount entry was updated in /etc/fstab.")
+	return a.offerMountNow(updated)
+}
+
+func (a *App) deleteClientMount(entries []FstabMountEntry) error {
+	entry, err := a.selectCIFSMount(entries)
+	if err != nil || entry == nil {
+		return err
+	}
+
+	confirm, err := a.confirm(fmt.Sprintf("Delete the mount for %s", entry.DisplayName), false)
+	if err != nil {
+		return err
+	}
+	if !confirm {
+		a.println("Delete cancelled.")
+		return nil
+	}
+
+	if err := a.writeFstabLineChange("", entry.LineIndex); err != nil {
+		return err
+	}
+
+	a.println("The mount entry was removed from /etc/fstab.")
+	return a.reloadSystemdIfNeeded()
+}
+
+func (a *App) selectCIFSMount(entries []FstabMountEntry) (*FstabMountEntry, error) {
+	if len(entries) == 0 {
+		a.println("There are no client mounts to select.")
+		return nil, nil
+	}
+
+	selection, err := a.prompt("Select mount number")
+	if err != nil {
+		return nil, err
+	}
+
+	index, err := strconv.Atoi(selection)
+	if err != nil || index < 1 || index > len(entries) {
+		a.println("Invalid selection.")
+		return nil, nil
+	}
+
+	entry := entries[index-1]
+	return &entry, nil
+}
+
+func cifsMountConfigFromEntry(entry FstabMountEntry) (CIFSMountConfig, bool) {
+	server, share, ok := splitCIFSSource(entry.Source)
+	if !ok {
+		return CIFSMountConfig{}, false
+	}
+
+	cfg := CIFSMountConfig{
+		Server:     server,
+		Share:      share,
+		MountPoint: entry.MountPoint,
+		AutoMount:  true,
+	}
+
+	for _, option := range entry.Options {
+		key, value, hasValue := strings.Cut(option, "=")
+		switch strings.ToLower(key) {
+		case "username":
+			if hasValue {
+				cfg.Username = unescapeFstabValue(value)
+			}
+		case "password":
+			if hasValue {
+				cfg.Password = unescapeFstabValue(value)
+			}
+		case "domain":
+			if hasValue {
+				cfg.Domain = unescapeFstabValue(value)
+			}
+		case "uid":
+			if hasValue {
+				cfg.UID = unescapeFstabValue(value)
+			}
+		case "gid":
+			if hasValue {
+				cfg.GID = unescapeFstabValue(value)
+			}
+		case "file_mode":
+			if hasValue {
+				cfg.FileMode = value
+			}
+		case "dir_mode":
+			if hasValue {
+				cfg.DirMode = value
+			}
+		case "ro":
+			cfg.ReadOnly = true
+		case "rw":
+			cfg.ReadOnly = false
+		case "noauto":
+			cfg.AutoMount = false
+		}
+	}
+
+	return cfg, true
+}
+
+func splitCIFSSource(source string) (server, share string, ok bool) {
+	unescaped := unescapeFstabValue(source)
+	if !strings.HasPrefix(unescaped, "//") {
+		return "", "", false
+	}
+
+	parts := strings.SplitN(strings.TrimPrefix(unescaped, "//"), "/", 2)
+	if len(parts) != 2 || strings.TrimSpace(parts[0]) == "" || strings.TrimSpace(parts[1]) == "" {
+		return "", "", false
+	}
+
+	return parts[0], parts[1], true
+}
+
+func (a *App) confirmAndWriteClientMount(line string, lineIndex int, promptLabel string) error {
+	a.println("")
+	a.println("Suggested /etc/fstab line:")
+	a.println(line)
+	a.println("")
+	a.println("This will store the username and password directly in /etc/fstab.")
+	a.println("That is simple for home use, but less secure than a credentials file.")
+	a.flush()
+
+	confirm, err := a.confirm(promptLabel, true)
+	if err != nil {
+		return err
+	}
+	if !confirm {
+		return nil
+	}
+
+	if err := a.writeFstabLineChange(line, lineIndex); err != nil {
+		return err
+	}
+	return a.reloadSystemdIfNeeded()
+}
+
+func (a *App) offerMountNow(cfg CIFSMountConfig) error {
+	mountNow, err := a.confirm("Try mounting it now", true)
+	if err != nil {
+		return err
+	}
+	if !mountNow {
+		return nil
+	}
+	if err := a.mountCIFS(cfg.MountPoint); err != nil {
+		return err
+	}
+	a.println("The network share was mounted.")
+	return nil
+}
+
+func (a *App) writeFstabLineChange(line string, lineIndex int) error {
+	data, err := os.ReadFile(a.fstabPath)
+	if err != nil {
+		return fmt.Errorf("read %s: %w", a.fstabPath, err)
+	}
+
+	updated, err := updateFstabContents(string(data), line, lineIndex)
+	if err != nil {
+		return err
+	}
+	return a.writeFstabContents(updated)
+}
+
+func updateFstabContents(contents, line string, lineIndex int) (string, error) {
+	hasTrailingNewline := strings.HasSuffix(contents, "\n")
+	lines := strings.Split(contents, "\n")
+	if len(lines) > 0 && lines[len(lines)-1] == "" {
+		lines = lines[:len(lines)-1]
+	}
+
+	switch {
+	case lineIndex < 0:
+		lines = append(lines, line)
+	case lineIndex >= len(lines):
+		return "", fmt.Errorf("mount entry line %d is out of range", lineIndex)
+	case line == "":
+		lines = append(lines[:lineIndex], lines[lineIndex+1:]...)
+	default:
+		lines[lineIndex] = line
+	}
+
+	updated := strings.Join(lines, "\n")
+	if hasTrailingNewline || updated != "" {
+		updated += "\n"
+	}
+	return updated, nil
+}
+
+func (a *App) writeFstabContents(serialized string) error {
+	backup := fmt.Sprintf("%s.bak.%s", a.fstabPath, time.Now().UTC().Format("20060102T150405Z"))
+
+	if err := copyFile(a.fstabPath, backup); err != nil {
+		if shouldOfferPrivilegeRetry(err) {
+			return a.writeFstabWithPrivilegeRetry(serialized, backup)
+		}
+		return friendlyWriteError("create backup", backup, err)
+	}
+
+	if err := os.WriteFile(a.fstabPath, []byte(serialized), 0o644); err != nil {
+		if shouldOfferPrivilegeRetry(err) {
+			return a.writeFstabWithPrivilegeRetry(serialized, backup)
+		}
+		return friendlyWriteError("write config", a.fstabPath, err)
+	}
+
+	return nil
+}
+
+func (a *App) writeFstabWithPrivilegeRetry(serialized, backup string) error {
+	a.println("")
+	a.println("Updating /etc/fstab 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("write config", a.fstabPath, os.ErrPermission)
+	}
+
+	retry, err := a.confirm("Retry updating /etc/fstab with sudo", true)
+	if err != nil {
+		return err
+	}
+	if !retry {
+		return friendlyWriteError("write config", a.fstabPath, os.ErrPermission)
+	}
+
+	tempPath, err := a.writeTempConfig(serialized)
+	if err != nil {
+		return fmt.Errorf("prepare fstab for sudo save: %w", err)
+	}
+	defer os.Remove(tempPath)
+
+	if err := a.runner.Run("sudo", "cp", a.fstabPath, backup); err != nil {
+		return friendlyWriteError("create backup", backup, err)
+	}
+
+	if err := a.runner.Run("sudo", "install", "-m", "644", tempPath, a.fstabPath); err != nil {
+		return friendlyWriteError("write config", a.fstabPath, err)
+	}
+
+	return nil
+}
+
 type ShareUserReference struct {
 	User   string
 	Shares []string

app_test.go

@@ -0,0 +1,88 @@
+package main
+
+import "testing"
+
+func TestParseCIFSMountEntries(t *testing.T) {
+	contents := `# comment
+UUID=1234 / ext4 defaults 0 1
+//fileserver/media /mnt/media cifs username=alice,password=p@\040ss\,word,iocharset=utf8,uid=1000,gid=1000,file_mode=0664,dir_mode=0775,rw 0 0
+//nas/backups /srv/backups smbfs username=bob,password=secret,noauto,ro 0 0
+`
+
+	entries := parseCIFSMountEntries(contents)
+	if len(entries) != 2 {
+		t.Fatalf("expected 2 CIFS entries, got %d", len(entries))
+	}
+
+	if entries[0].LineIndex != 2 {
+		t.Fatalf("unexpected first line index: %d", entries[0].LineIndex)
+	}
+	if entries[0].Source != "//fileserver/media" {
+		t.Fatalf("unexpected first source: %q", entries[0].Source)
+	}
+	if entries[0].MountPoint != "/mnt/media" {
+		t.Fatalf("unexpected first mount point: %q", entries[0].MountPoint)
+	}
+	if entries[1].FSType != "smbfs" {
+		t.Fatalf("unexpected second fs type: %q", entries[1].FSType)
+	}
+}
+
+func TestCIFSMountConfigFromEntry(t *testing.T) {
+	entry, ok := parseFstabMountLine("//fileserver/media /mnt/media cifs username=alice,password=p@\\040ss\\,word,domain=WORKGROUP,uid=1000,gid=1000,file_mode=0664,dir_mode=0775,noauto,ro 0 0", 0)
+	if !ok {
+		t.Fatal("expected line to parse")
+	}
+
+	cfg, ok := cifsMountConfigFromEntry(entry)
+	if !ok {
+		t.Fatal("expected config conversion to succeed")
+	}
+
+	if cfg.Server != "fileserver" || cfg.Share != "media" {
+		t.Fatalf("unexpected source parsing: %+v", cfg)
+	}
+	if cfg.Password != "p@ ss,word" {
+		t.Fatalf("unexpected password: %q", cfg.Password)
+	}
+	if cfg.Domain != "WORKGROUP" {
+		t.Fatalf("unexpected domain: %q", cfg.Domain)
+	}
+	if cfg.AutoMount {
+		t.Fatal("expected noauto to disable automount")
+	}
+	if !cfg.ReadOnly {
+		t.Fatal("expected ro to set read-only")
+	}
+}
+
+func TestUpdateFstabContentsAddEditDelete(t *testing.T) {
+	initial := "# header\nUUID=1234 / ext4 defaults 0 1\n//old/share /mnt/share cifs username=old,password=old,rw 0 0\n"
+
+	added, err := updateFstabContents(initial, "//new/share /mnt/new cifs username=new,password=new,rw 0 0", -1)
+	if err != nil {
+		t.Fatalf("add entry: %v", err)
+	}
+	wantAdded := "# header\nUUID=1234 / ext4 defaults 0 1\n//old/share /mnt/share cifs username=old,password=old,rw 0 0\n//new/share /mnt/new cifs username=new,password=new,rw 0 0\n"
+	if added != wantAdded {
+		t.Fatalf("unexpected add result:\nwant: %q\ngot:  %q", wantAdded, added)
+	}
+
+	edited, err := updateFstabContents(initial, "//old/share /mnt/share cifs username=alice,password=secret,ro 0 0", 2)
+	if err != nil {
+		t.Fatalf("edit entry: %v", err)
+	}
+	wantEdited := "# header\nUUID=1234 / ext4 defaults 0 1\n//old/share /mnt/share cifs username=alice,password=secret,ro 0 0\n"
+	if edited != wantEdited {
+		t.Fatalf("unexpected edit result:\nwant: %q\ngot:  %q", wantEdited, edited)
+	}
+
+	deleted, err := updateFstabContents(initial, "", 2)
+	if err != nil {
+		t.Fatalf("delete entry: %v", err)
+	}
+	wantDeleted := "# header\nUUID=1234 / ext4 defaults 0 1\n"
+	if deleted != wantDeleted {
+		t.Fatalf("unexpected delete result:\nwant: %q\ngot:  %q", wantDeleted, deleted)
+	}
+}