I frequently deploy pre-releases of our software to help test and provide early feedback to our Engineering teams. One piece of software that I deploy some what frequently is our ESXi Hypervisor and the best way to deploy it, is of course inside of a Virtual Machine or commonly referred to as Nested ESXi.

Most recently while testing a new ESXi build in my lab (screenshot below is for demo purposes, not the actual PSOD image), I encountered an ESXi purple screen of death (PSOD) during the bootup of the ESXi Installer itself. Since ESXi had not been installed, there was no place for ESXi to actually store the core dumps which made it challenging when filing a bug with Engineering as screenshots may not always contain all the necessary details.

Luckily, because we are running in a VM, a really neat feature that VMware has supported for quite some time now is configuring a virtual serial port for logging purposes. In fact, one of the neatest feature from a troubleshooting standpoint was the introduction of the Virtual Serial Port Concentrator (vSPC) feature in vSphere 5.0 which allowed a VM to log directly to a serial console server just like you would for physical servers. You of course had few other options of either logging directly to the serial port of the physical ESXi, named pipe or simply to a file that lived on a vSphere Datastore.

Given this was a home lab setup, the easiest method was to simply output to a file. To add a virtual serial port, you can either use the vSphere Web/C# Client or the vSphere APIs. Since this is not something I need to do often, I just used the UI. Below is a screenshot using the vSphere Web Client and once you have added the virtual serial port, you need to specify the filename and where to the store the output file by clicking on the "Browse" button.

If the GuestOS which includes ESXi has been configured to output to a serial port, the next time there is an issue and you can easily captured the output to a file instead of just relying on a screenshot. One additional tip which might be useful is by default, vSphere will prompt whether you want to replace or append to the configured output file. If you wish to always replace, you can add the following VM Advanced Setting and you will not get prompted in the UI.

answer.msg.serial.file.open = "Replace"

Virtual serial ports are supported on both vSphere (vCenter Server + ESXi) as well as our hosted products VMware Fusion and Workstation.