Enable xterm.js on Proxmox VM

1. Add a virtual serial port to your VM: qm set YOUR_VM_ID -serial0 socket
2. Log in to your VM and configure: sudo vim /etc/default/grub
3. Replace the line GRUB_CMDLINE_LINUX_DEFAULT=… with:

   GRUB_CMDLINE_LINUX_DEFAULT="quiet console=tty0 console=ttyS0,115200"	
   

4. Update grub: sudo update-grub
5. Shutdown shutdown -h now and Start the VM
6. Either open it from the Proxmox Web UI or on the PVE host issue: qm terminal YOUR_VM_ID

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Relevant Note(s): Proxmox Setup