How to Use the OH Tool on the Windows NT 4.0 Resource Kit

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This article discusses the OH monitoring tool OH (Oh.exe) that is included in the Microsoft Windows NT Server 4.0 Resource Kit Supplement Two. The OH utility can help monitor which files, registry keys, and directories are in use by certain services at any given time.


This command-line tool shows the handles of all open windows. Alternatively, you can constrain the OH display to show only information relating to a particular process, object type, or object name. This feature is useful when a sharing violation occurs because you can find the process that has a file open at the time of violation.

To function properly, OH requires that an option internal to the Windows NT kernel be enabled. This option maintains a linked list of all objects by object type. If OH detects that this option is not set, OH sets it and sends a message that the user must restart the computer before the option will take effect. After restarting, OH can give useful results.

This linked list costs 8 bytes of overhead for each object. If desired, this option can later be disabled with Gflags.exe (in the Windows NT 4.0 Resource Kit) by clearing the check box for" Maintain a list of objects for each type" in the Global Flags window, then restarting the system.

The most convenient way to use OH is to have it pipe the data to a text file. At the command prompt type:
Oh >***.txt {where *** is the name you provide}
To view the data, open the file with Notepad.


For additional information about the OH utility, type the following line at a command prompt type, and then press ENTER:
Use OH /?


Article ID: 172710 - Last Review: November 1, 2006 - Revision: 1.1
  • Microsoft Windows NT Workstation 4.0 Developer Edition
  • Microsoft Windows NT Server 4.0 Standard Edition
kbinfo kbtool KB172710

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