Microsoft KB Archive/164471

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Replacing System Files Using a Modified Emergency Repair Disk

Article ID: 164471

Article Last Modified on 11/1/2006


  • Microsoft Windows NT Workstation 3.51
  • Microsoft Windows NT Workstation 4.0 Developer Edition
  • Microsoft Windows NT Server 3.51
  • Microsoft Windows NT Server 4.0 Standard Edition

This article was previously published under Q164471


The Windows NT Setup program and Emergency Repair Disk (ERD) can be used to replace operating system files that cannot be copied by simpler means. This procedure is most useful if an installation of Windows NT is on an NTFS partition that has been rendered unbootable. This procedure can also be used to replace files on a mirrored partition without first breaking the mirror.


This procedure can be used to replace any Windows NT system file. In this example we replace the file \WINNT\system32\drivers\beep.sys. Note that the file Beep.sys is just an example. Any other Windows NT system file can be replaced if the correct path and filename is used. An Emergency Repair Disk from the installation of Windows NT that we are replacing the file on is required for this operation. It is possible to use an ERD from an identical installation of Windows NT on another computer, but this invites unforeseen problems if there is even a minor difference between installations.

NOTE: To use the NT V4.0 Emergency Repair Disk utility, you must have the updated version of Setupdd.sys. The updated version is contained in NT v4.0 Service Pack 2 or later. To update your version of Setupdd.sys, you must copy Setupdd.sys from the Service Pack to your NT v4.0 Setup disk 2. This replaces the previous version of Setupdd.sys with the updated version.

For more information, please see the following article(s) in the Microsoft Knowledge Base:

ARTICLE-ID: 168015
TITLE : Files Not Replaced When Running Emergency Repair.

  1. The Emergency Repair Disk is created during the initial Setup of Windows NT, or by running the Windows NT RDISK.EXE program. Copy the contents of the original ERD onto another diskette or subdirectory on another machine as a backup. The original ERD information saved should be restored unmodified to the original ERD in case this procedure is unsuccessful or there is ever a need to return to the configuration that was originally saved.
  2. Remove the read only attribute on the Setup.log file. This is a hidden, system file on the ERD that can be edited with a text editor. Alter the Setup.log file as in the sample below, replacing the entire [Files.WinNt] section with an entry like the last line in the example. Additional lines can be included if more than one file needs to be copied. The [Files.WinNt] section of Setup.log contains an entry for every Windows NT operating system file. When creating or modifying the entry make sure the target folder for the file is the same as the TargetDirectory value in line one of the [Paths] section. The target folder corresponds to the Windows NT systemroot.

    This can easily be done by finding and modifying the original line for the target file in the [Files.WinNT] section.

    The original line in the Setup.log will be similar to:

    \WINNT\system32\drivers\beep.sys = "beep.sys","f7fb"

    Modified to replace the file from the ERD instead of the CD it looks like (this line is wrapped for appearances only):

    \WINNT\system32\drivers\beep.sys = "beep.sys","99999","\","ERD disk","beep.sys"

    The entry 99999 replaces the checksum f7fb that the original ERD used. This insures that the repair process will prompt you to replace this file. The "\" indicates that the repair process should look to the Root of the disk to copy the file from. "ERD disk" is used to prompt the user for the ERD if it is not in the drive when Setup needs to copy it. The last entry in the line is the file name as it appears on the ERD and is used as a tag file to ensure the proper disk is inserted to copy the files from.

    Here is an example of the entire contents of a Setup.log file after it has been modified:

          TargetDirectory = "\WINNT"
          TargetDevice = "\Device\Harddisk1\partition1"
          SystemPartitionDirectory = "\"
          SystemPartition = "\Device\Harddisk0\partition1"
          Version = "WinNt4.0"
          NTBOOTDD.SYS = "sparrow.sys","b4a3"
          ntldr = "ntldr","2a36b"
          NTDETECT.COM = "NTDETECT.COM","b69e"
          \WINNT\system32\drivers\tcpip.sys = "beep.sys","99999","\","ERD
  3. Copy the file (in this case Beep.sys) to the root of the ERD. If there is not enough room on the ERD for the file you are replacing, any files other than Setup.log can be deleted from the ERD to make room. This makes the ERD unusable for other repair functions, so keep the original ERD in a safe place. You can also use a second disk containing the file to be replaced and insert it when prompted for "ERD disk."

    NOTE: The above line will replace Tcpip.sys with the file Beep.sys thus overwriting the original Tcpip.sys file. This example demonstrates the added capability of the ERD to replace any file with any other file.
  4. Run Windows NT Setup and select the repair option to replace the file. This is standard procedure from here; the rest of the steps are a review of the repair process.
  5. Run Windows NT setup. Most likely this will be done from the boot disks. Select R for repair in the first "Welcome to Setup" screen. Deselect all but "Verify Windows NT system files" in the next screen and then select continue. Note that the repair process in Windows NT 4.0 requires a CD-ROM drive on the target computer and a copy of the Windows NT 4.0 CD. If these are not available, please see the following article in the Microsoft Knowledge Base:

    ARTICLE-ID: 158423
    TITLE : WinNT 4.0 ERD Won't Allow Repair w/out Compact Disc Installed

  6. When prompted for the Emergency Repair Disk, put the modified copy of the ERD in drive A: and press Enter.
  7. Setup reports that the file you are replacing is not from the original Windows NT installation. Press Enter to replace the file. Setup reports that it has completed repairs. Press Enter to restart the computer.

If the procedure fails check for these common errors:

  • Is the full path of the file correct? This will happen if you change the filename in the example but not its path.
  • Does the target directory of the file match the TargetDirectory Value at the top of Setup.log?
  • Are all the items in the correct order on the modified Setup.log entry?
  • Are there any typographical errors? Are all items in quotes as they are in the example?
  • Are all commas entered as in the example?
  • Did you exit Setup (f3) after replacing the desired files from floppy. If not it may have been replaced again further down the files list if you did not remove them as described in step 2.

Additional query words: 4.00 prodnt

Keywords: kbhowto kbsetup KB164471