serial/COM port pass through on ESXi 4.1

I have a virtual machine that needs to use the COM port that is on the main board of the ESXi host.  Can I do COM/Serial port pass through.  I need to send ASCII characters to the VM via this port.  
Who is Participating?

[Product update] Infrastructure Analysis Tool is now available with Business Accounts.Learn More

I wear a lot of hats...

"The solutions and answers provided on Experts Exchange have been extremely helpful to me over the last few years. I wear a lot of hats - Developer, Database Administrator, Help Desk, etc., so I know a lot of things but not a lot about one thing. Experts Exchange gives me answers from people who do know a lot about one thing, in a easy to use platform." -Todd S.

Andrew Hancock (VMware vExpert / EE MVE^2)VMware and Virtualization ConsultantCommented:
Yes, this works very well; we use for debugging serial communications.

 Serial Port
Just make sure that the SERIAL port is enabled in the BIOS of the VM, and set to COM1 or COM2 etc, sometimes, change from auto to ENABLE.

Experts Exchange Solution brought to you by

Your issues matter to us.

Facing a tech roadblock? Get the help and guidance you need from experienced professionals who care. Ask your question anytime, anywhere, with no hassle.

Start your 7-day free trial
Andrew Hancock (VMware vExpert / EE MVE^2)VMware and Virtualization ConsultantCommented:
I have a serial-connected device to a VM. It uses the same setting as you stated (/dev/ttyS0). You can only have one VM using the physical host's serial connection, though. (see: If you have issues Get the hostd logs and see if it shows us anything (see:

Normally the Default Operation for Serial Poirts in the Virtual Machine BIOS are set to AUTO.

AUTO - Bios or OS choose configuration.

 VM Serial Ports
Just remember to enable serial ports in the VM BIOS, and VM OS!
gopher_49Author Commented:
Okay. I'll convert the physical machine to a VM and give it a shot.  I'll know something tomorrow
Big Business Goals? Which KPIs Will Help You

The most successful MSPs rely on metrics – known as key performance indicators (KPIs) – for making informed decisions that help their businesses thrive, rather than just survive. This eBook provides an overview of the most important KPIs used by top MSPs.

gopher_49Author Commented:
In the BIOS I specified COM 1, however, Windows is showing COM2 and COM3.  I don't see anywhere in the VM settings to force a specified COM port.  I'll change my app to look on COM2, however, I figured it would show up as COM1 since I specified COM1 in the BIOS.
gopher_49Author Commented:
It works...  I changed my app to use COM2 and it's receiving data.  I guess the Windows mapping doesn't match the COM port noted in the BIOS, however, the physical hardware ID configured in the VM matches the hardward ID of COM1 noted in the BIOS.  I guess when it mapped it to Windows it changed the logical COM port number?!  Either way...  It works...
Andrew Hancock (VMware vExpert / EE MVE^2)VMware and Virtualization ConsultantCommented:
There is none, COM ports are allocated by I/O address, like in the good old days of DOS! They are allocated at BIOS level. Windows will then do the plug and play!

It's possible the difference between actual physical IO ports, and Logical Name ports!

COM1 is normally 3F8, COM2 is normally 2F8, but Windows gets COM ports confused, and just adds COM2, COM3 etc

As long as you've got data, being received.
gopher_49Author Commented:
I noticed in the client it shows /dev/char/serial/uart0 as the selected COM port, however, it also shows /uart1/ but there is only one COM port on this server?!  Maybe there is another and I didn't noticed it.  Anyway, I guess Windows got confused and added COM2... Either way.. It works.

It's more than this solution.Get answers and train to solve all your tech problems - anytime, anywhere.Try it for free Edge Out The Competitionfor your dream job with proven skills and certifications.Get started today Stand Outas the employee with proven skills.Start learning today for free Move Your Career Forwardwith certification training in the latest technologies.Start your trial today

From novice to tech pro — start learning today.