Linux | Guidelines for setting up a Linux Server as a VM

These are just plain guidelines for setting up a Linux server as a virtual machine. As time passes I keep seeing the same mistakes from fellow admins, over and over again so I decided to mention some of it.

Feel free to add anything else in the comments or point me out should I am making a mistake somewhere along the way ;)

First things first, you have to decide what will be the use of the VM that you are creating? Will it be a file server, or a web server, or a database server? Perhaps it will be a dedicated VM for a couple of users. No matter your choice, if you are setting up the server as a virtual machine in you infrastructure you have to keep in mind a few things so these are just a few golden rules for setting up a Linux VM so that you don't end up crying later when things go bad.

vSphere | Virtual Machine that is neither powered on nor powered off

I had a very interesting problem with a VM for which I concluded being in a phantom state, that is a VM that is neither powered on, nor powered off. No matter what you try to do to the VM you always end up with error message that says:

The attempted operation cannot be performed in the current state: Powered ON.

The thing is, that if you try to access the console, the machine is not powered on. Even more, if you open the VMRC you could end up seeing an error message:

Unable to connect to the MKS: The operation is not allowed in the current state.

So what should I do? I decided to hit the ESXi Shell. VMware has a pretty nice KB article and even a video on what to do when you encounter this problem:

ESXi 5.5 | KB 1014165

Connect to the host using an SSH client and try the steps described into that article. However if the VM still cannot be powered off than you must reboot the ESXi host in order to refresh the VM state.

If this happens too often then you must consider moving everything off that host, as this probably indicates problems with the host itself.

vSphere | A VM is showing disk size of 0B

Being given a task to figure out and clean up the mess of a poorly maintained vSphere Infrastructure a while ago, i encountered a very strange problem.

They informed me that the Veeam Backup failed for that VM, and the error message was:

Virtual disk configuration change detected, resetting CBT failed Details: A general system error occurred: 
Creating VM snapshot
Error: A general system error occurred: