The virtual machine serial console in the Azure portal provides access to a text-based console for Windows virtual machines. This serial connection connects to the COM1 serial port of the VM providing access to it, independent of the virtual machine's network or operating system state. Access to the serial console for the VM can be done only by using the Azure portal.
You have to have an access role of Virtual Machine Contributor or higher to access the virtual machine.
Special Administrative Console (SAC) is supported on server versions of Windows but isn't available on client versions.
To access it, navigate to the virtual machines and select the VM with which you want to access SAC, drill down to Support + Troubleshooting and select Serial Console
Once SAC is available the SAC> prompt will become available
Typing help and hitting enter will return these troubleshooting options
If you need to get to command prompt or PowerShell you need to create a channel that has a CMD instance so that you can troubleshoot your instance further, enter;
To switch to the channel that's running the CMD instance, enter the following;
ch -si 1
Enter the sign-in credentials with administrative permissions, after you've entered valid credentials, the CMD instance opens.
To start a PowerShell instance, enter PowerShell within the cmd instance then press Enter.
For example windows and PowerShell commands, see https://docs.microsoft.com/en-us/troubleshoot/azure/virtual-machines/serial-console-cmd-ps-commands
Disable SAC on the VM
The serial console can be disabled for a specific VM by disabling that VM's boot diagnostics setting. Turn off boot diagnostics from the Azure portal to disable the serial connection.