MODIFYING THE REGISTRY

4-27Lesson 3 Troubleshooting Problems Using Startup and Recovery Tools

Guidelines for Troubleshooting Startup Using the Last Known Good

Configuration

Selecting the Last Known Good configuration advanced boot option starts Windows XP

Professional using the control set saved to the Registry following the last successful

logon. If you change the Windows XP Professional configuration to load a driver and

have problems rebooting, you can use the Last Known Good configuration to recover

your working configuration.

Windows XP Professional provides two configurations for starting a computer, Default

and Last Known Good. Figure 4-5 shows the events that occur when you make config-

uration changes to your system. Any configuration changes (for example, adding or

removing drivers) are saved in the Current control set.

MapaddressesVirtual address spacePhysical memorySwap memoryDiskcontents

F04us05

Figure 4-5

Default and Last Known Good are the two available startup configurations.

After you reboot the computer, the kernel copies the information in the Current control

set to the Clone control set during the kernel initialization phase. When you success-

fully log on to Windows XP Professional, the information in the Clone control set is

copied to the Last Known Good control set, as shown in the lower part of Figure 4-5.

If you experience startup problems that you think might relate to Windows XP Profes-

sional configuration changes, shut down the computer without logging on, and then

restart it. When you are prompted to select the operating system to start from a list of the

operating systems specified in the BOOT.INI file, press F8 to open the Windows

Advanced Options Menu screen. Then select the Last Known Good Configuration option.

!

Exam Tip The Safe Mode and Last Known Good Configuration options are two of the most

useful tools to try first when troubleshooting Windows startup. Enabling Boot Logging is also

useful, typically when you are having trouble locating the source of the problem.

The next time you log on, the Current configuration is copied to the Default configura-

tion. If your configuration changes work correctly, the next time you log on, the Current

configuration is copied to the Default configuration. If your configuration changes do

not work, you can restart and use the Last Known Good Configuration option to log on.

Table 4-9 summarizes the purpose of the Default and Last Known Good configurations.

Table 4-9

Default and Last Known Good Configurations

Configuration Description

Default Contains information that the system saves when a computer shuts down.

To start a computer using the default configuration, select Windows XP

Professional on the Please Select The Operating System To Start menu.

Last Known Good Contains information that the system saves after a successful logon. The

Last Known Good configuration loads only if the system is recovering from

a severe or critical device driver loading error or if it is selected during the

boot process.

Table 4-10 lists situations in which you can use the Last Known Good configuration

and the related solutions.

Table 4-10

When to Use the Last Known Good Configuration

Situation Solution

Use the Last Known Good configuration option to start Windows

After a new device driver is

XP Professional because the Last Known Good configuration

installed, Windows XP

does not contain any reference to the new (possibly faulty)

Professional restarts, but the

driver.

system stops responding.

Some critical drivers are written to keep users from making the

You accidentally disable a

critical device driver (such

mistake of disabling them. With these drivers, the system auto-

as the Scsiport driver).

matically reverts to the Last Known Good control set if a user

disables the driver. If the driver does not automatically cause the

system to revert to the Last Known Good control set, you must

manually select the Last Known Good Configuration option.

Using the Last Known Good configuration does not help in the following situations:

■

When the problem is not related to Windows XP Professional configuration

changes. Such a problem might arise from incorrectly configured user profiles or

incorrect file permissions.

■

After you log on. The system updates the Last Known Good control set with Win-

dows XP Professional configuration changes after a successful logon.

■

When startup failures relate to hardware failures or missing or corrupted files.