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 Recreate Corrupt Hive

 Regrecover can open any registry file, no matter how corrupted it may be. It linearly reads all data that are still available and then rebuilds their structure. The rebuilt structure can be exported into a new, non-corrupt hive. The recreated hive can be used as a replacement for the corrupted one if (and only if) all essential data are still available. When running "Estimate size of recreated hive" the result should not be less than about 90 percent of the original file size. The new hive contains the sub keys of the root key, but not the disconnected keys. The latter can be exported into template reg files, which then have to be edited by the user before they can be imported back into the hive.

 For a SOFTWARE hive, any installed software should have a corresponding sub key, and if this key, or its subkeys, are missing that software will have to be reinstalled. Furthermore, the sub keys

   SOFTWARE\Classes,
   SOFTWARE\Classes\CLSID, and
   SOFTWARE\Classes\Interface

should have no obvious gaps in the alphabetic list of their sub keys:

       


 If a system won’t boot up with a recreated SYSTEM hive, one could still try one of the following:

  • select a different default ControlSet key
  • merge one of the other ControlSet keys into the default ControlSet key.
Suppose for example the hive looks like this:

   

In general, when a system boots up, only one of the ControlSet keys is used and is copied to the CurrentControlSet key. Which one is used is determined by the 'Default' value of the Select key, so in the example above ControlSet001 is used. If that value is changed from 1 to 2 then Controlset002 will be used instead (see MS KB 100010 for more details). This will solve the problem if all essential information is still in ControlSet002.
It may well happen that both ControlSet keys are damaged, but at different positions. Then merging, for example, ControlSet002 into ControlSet001 could still give a working hive. To merge the keys, first load a copy of the file as a hive by Regedit to a temporary key, say to HKEY_USERS\sys. Then load a copy of the file by Regrecover and interchange the names by renaming

   ControlSet001 ControlSet000
   ControlSet002 ControlSet001
   ControlSet000 ControlSet002

Then rename the root key to HKU\sys, so that it corresponds to the hive loaded by Regedit:

   

Now right click Controlset001 and select 'Merge Folder into Registry'. When done close Regrecover and unload the hive by Regedit. It now contains the merged key, merged as far as allowed by the present access rights.


 When recreating a hive on W2k or NT4 one has to assure that the maximum registry size is at least the current registry size plus the size of the opened file. Otherwise an error message like ”Insufficient system resources exist to complete the requested service” will pop up. To increase the maximum registry size

   

on W2k or NT4 go to System Properties Advanced Performance Options, and click 'Change'. The corresponding Registry value is named 'RegistrySizeLimit' at HKLM\SYSTEM\CurrentControlSet\Control.
   
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