What is the Registry?

The windows registry provides for a somewhat secure, unified database that stores configuration information into a hierarchical model. Until recently, configuration files such as WIN.INI, were the only way to configure windows applications and operating system functions. In todays NT 4 environment, the registry replaces these .INI files. Each key in the registry is similar to bracketed headings in an .INI file.

One of the main disadvantages to the older .INI files is that those files are flat text files, which are unable to support nested headings or contain data other than pure text. Registry keys can contain nested headings in the form of subkeys. These subkeys provide finer details and a greater range to the possible configuration information for a particular operating system. Registry values can also consist of executable code, as well as provide individual preferences for multiple users of the same computer. The ability to store executable code within the Registry extends its usage to operating system system and application developers. The ability to store user-specific profile information allows one to tailor the environment for specific individual users.

To view the registry of an NT server, one would use the Registry Editor tool. There are two versions of Registry Editor:

.:Regedt32.exe has the most menu items and more choices for the menu items. You can search for keys and subkeys in the registry.

.:Regedit.exe enables you to search for strings, values, keys, and subkeys and export keys to .reg files. This feature is useful if you want to find specific data.

For ease of use, the Registry is divided into five seperate structures that represent the Registry database in its entirety. These five groups are known as Keys, and are discussed below:

In Depth Key Discussion

HKEY_CURRENT_USER

 This registry key contains the configuration information for the user that is currently logged in. The users folders, screen colors, and control panel settings are stored here. This information is known as a User Profile.

HKEY_USERS

 In windowsNT 3.5x, user profiles were stored locally (by default) in the systemroot\system32\config directory. In NT4.0, they are stored in the systemroot\profiles directory. User-Specific information is kept there, as well as common, system wide user information.

This change in storage location has been brought about to parallel the way in which Windows95 handles its user profiles. In earlier releases of NT, the user profile was stored as a single file - either locally in the \config directory or centrally on a server. In windowsNT 4, the single user profile has been broken up into a number of subdirectories located below the \profiles directory. The reason for this is mainly due to the way in which the Win95 and WinNT4 operating systems use the underlying directory structure to form part of their new user interface.

A user profile is now contained within the NtUser.dat (and NtUser.dat.log) files, as well as the following subdirectories:

* Application Data: This is a place to store application data specific to this particular user.

* Desktop: Placing an icon or a shortcut into this folder causes the that icon or shortcut to appear on the desktop of the user.

* Favorites: Provides a user with a personlized storage place for files, shortcuts and other information.

* NetHood: Maintains a list of personlized network connections.

* Personal: Keeps track of personal documents for a particular user.

* PrintHood: Similar to NetHood folder, PrintHood keeps track of printers rather than network connections.

* Recent: Contains information of recently used data.

* SendTo: Provides a centralized store of shortcuts and output devices.

* Start Menu: Contains configuration information for the users menu items.

* Templates: Storage location for document templates.

HKEY_LOCAL_MACHINE

 This key contains configuration information particular to the computer. This information is stored in the systemroot\system32\config directory as persistent operating system files, with the exception of the volatile hardware key.

 The information gleaned from this configuration data is used by applications, device drivers, and the WindowsNT 4 operating system. The latter usage determines what system configuration data to use, without respect to the user currently logged on. For this reason the HKEY_LOCAL_MACHINE regsitry key is of specific importance to administrators who want to support and troubleshoot NT 4.

HKEY_LOCAL_MACHINE is probably the most important key in the registry and it contains five subkeys:

* Hardware: Database that describes the physical hardware in the computer, the way device drivers use that hardware, and mappings and related data that link kernel-mode drivers with various user-mode code. All data in this sub-tree is re-created everytime the system is started.

* SAM: The security accounts manager. Security information for user and group accounts and for the domains in NT 4 server.

* Security: Database that contains the local security policy, such as specific user rights. This key is used only by the NT 4 security subsystem.

* Software: Pre-computer software database. This key contains data about software installed on the local computer, as well as configuration information.

* System: Database that controls system start-up, device driver loading, NT 4 services and OS behavior.

Information about the HKEY_LOCAL_MACHINE\SAM Key

This subtree contains the user and group accounts in the SAM database for the local computer. For a computer that is running NT 4, this subtree also contains security information for the domain. The information contained within the SAM registry key is what appears in the user interface of the User Manager utility, as well as in the lists of users and groups that appear when you make use of the Security menu commands in NT4 explorer.

Information about the HKEY_LOCAL_MACHINE\Security key

This subtree contains security information for the local computer. This includes aspects such as assigning user rights, establishing password policies, and the membership of local groups, which are configurable in User Manager.

HKEY_CLASSES_ROOT

 The information stored here is used to open the correct application when a file is opened by using Explorer and for Object Linking and Embedding. It is actually a window that reflects information from the HKEY_LOCAL_MACHINE\Software subkey.

HKEY_CURRENT_CONFIG

 The information contained in this key is to configure settings such as the software and device drivers to load or the display resolution to use. This key has a software and system subkeys, which keep track of configuration information.

Understanding Hives

 The registry is divided into parts called hives. These hives are mapped to a single file and a .LOG file. These files are in the systemroot\system32\config directory.

Registry Hive                                                    File Name

=================================================================

HKEY_LOCAL_MACHINE\SAM                          SAM and SAM.LOG

HKEY_LOCAL_MACHINE\SECURITY                 Security and Security.LOG

HKEY_LOCAL_MACHINE\SOFTWARE               Software and Software.LOG

HKEY_LOCAL_MACHINE\SYSTEM                    System and System.ALT

=================================================================

Although I am not gauranteeing that these files will be easy to understand, with a little research and patience, you will learn what you want to learn. I have been asked to write a file on how to decipher the contents of those files, but I have yet to decide weather I will do it or not.

Quick Notes

Ownership = The ownership menu item presents a dialog box that identifies the user who owns the selected registry key. The owner of a key can permit another user to take ownership of a key. In addition, a system administrator can assign a user the right to take ownership, or outright take ownership himself.

REGINI.EXE = This utility is a character based console application that you can use to add keys to the NT registry by specifying a Registry script.

Default Registry Settings

 The Following table lists the major Registry hives and some subkeys and the DEFAULT access permissions assigned:

\\ denotes a major hive        \denotes a subkey of the prior major hive

\\HKEY_LOCAL_MACHINE

                        Admin-Full Control

                        Everyone-Read Access

                        System-Full Control

 \HARDWARE

                        Admin-Full Control

                        Everyone-Read Access

                        System-Full Control

\SAM

                        Admin-Full Control

                        Everyone-Read Access

                        System-Full Control

\SECURITY

                        Admin-Special (Write DAC, Read Control)

                        System-Full Control

 \SOFTWARE

                        Admin-Full Control

                        Creator Owner-Full Control

                        Everyone-Special (Query, Set, Create, Enumerate, Notify, Delete, Read)

                        System-Full Control

\SYSTEM

                        Admin-Special (Query, Set, Create, Enumerate, Notify, Delete, Read)

                        Everyone-Read Access

                        System-Full Control

\\HKEY_CURRENT_USER

                        Admin-Full Control

                        Current User-Full Control

                        System-Full Control

\\HKEY_USERS

                        Admin-Full Control

                        Current User-Full Control

                        System-Full Control

\\HKET_CLASSES_ROOT

                        Admin-Full Control

                        Creator Owner-Full Control

                        Everyone-Special (Query, Set, Create, Enumerate, Notify, Delete, Read)

                        System-Full Control

\\HKEY_CURRENT CONFIG

                        Admin-Full Control

                        Creator Owner-Full Control

                        Everyone-Read Access

                        System-Full Control