File and Folder Access Controls in Mac OS 9

Mac OS 9 relied on a hybrid system of access controls that combined traditional Finder file attributes, AppleShare network permissions applied to local folders, and a native "Multiple Users" security environment. Because the underlying file systems (HFS and HFS+) lacked the native POSIX-style user permissions found in modern Unix-based systems like macOS, Mac OS 9 regulated access through file-level state flags, password-based file encryption, folder-level sharing privileges, and system-level environment restrictions.

File-Level Attributes and Protection

On an individual file level, standard users had limited options to restrict access without third-party tools, primarily relying on basic Finder settings and built-in utilities:

  • Locked Attribute: Accessible via the "Get Info" window (Command-I), checking the "Locked" box prevented the file from being modified, renamed, or moved to the Trash. While it guarded against accidental overwrites or deletion, any user with physical access could simply uncheck the box to regain full control.
  • Apple File Security (Encryption): Mac OS 9 introduced native file encryption. By selecting a file and using the contextual menu or the Apple File Security utility, users could encrypt individual files with a passphrase using either standard 40-bit or 56-bit DES encryption (with 128-bit available in certain configurations). Encrypted files could not be opened without the designated passphrase.
  • Stationery Pad: This toggle, also located in the "Get Info" window, forced a document to open as an untitled copy. While not a strict security permission, it protected the original template file from being directly overwritten by subsequent saves.

Folder-Level Sharing and AppleShare Privileges

Mac OS 9 used the AppleShare permission model for local folders, which became fully active when File Sharing was turned on. Applied through the "Sharing" pane of a folder's "Get Info" window, access was assigned across three entity tiers: Owner, User/Group, and Everyone.

For each tier, administrators could toggle three specific privileges:

  • See Folders: Allowed users to see subfolders located inside the selected folder.
  • See Files: Allowed users to see and open the files contained within the folder.
  • Make Changes: Allowed users to save new files, edit existing contents, or delete items inside the folder.

Additionally, folders featured a protection checkbox labeled "Can't move, rename, or delete this item." This prevented any user, including the owner, from modifying the folder's container status without first deliberately unchecking the option. An option to propagate permissions to all enclosed folders was also provided.

The "Multiple Users" Control Panel

To address the lack of true multi-user isolation on local machines, Mac OS 9 introduced the Multiple Users control panel. This feature created virtual boundaries for accounts classified into three types:

  • Normal: Standard account with full access to files, applications, and system settings.
  • Limited: Restricted access to specific applications and control panels defined by the administrator. Limited users were given a private "Documents" folder, and access to other users' private folders was blocked by the Finder.
  • Panels: A simplified interface replacing the standard Finder desktop with tabbed panels. Users could only access explicitly authorized applications and their designated personal folder, preventing direct navigation of the broader file system and root volume.