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vCOM is a free utility to create virtual serial port pairs which can be used to capture the debug output of ReactOS and direct it to a terminal program.

Useful terminal programs that are able to get this output include:


Get vCOM, extract it and install it by using hdwwiz or devcon install.

It will automatically install a pair of virtual COM ports "COM4" and "COM5" that are linked by a virtual Null Modem Cable.

You are done.

Connecting the Virtual Machine and Terminal Application

Connect the Virtual Machine to your first virtual port ("COM4" or \\.\COM4) and the terminal application to the second ("COM5" or \\.\COM5).

The properties of the serial port (usually specified in the virtual machine), like the baud rate, are not important. Instead, be sure to select "NO FLOW CONTROL", because otherwise the terminal app won't receive any characters.

What does vCOM do?

Com0com sys.png

^ This is only temporary until someone can change it with one that mentions vCOM instead of com0com.

The Virtual Machine shows a COM1 port to ReactOS which is used for sending debug messages.

The Virtual Machine then maps this port to a virtual port that is visible to the host Operating System.

vCOM emulates a Null Modem Cable between the VM and the Terminal Application.