How to fix "unable to find a serial interface" when using qm terminal (Proxmox)

[hotfuzz]

When using QEMU server configured by Proxmox, I received an error: "unable to find a serial interface" after running qm terminal.

According to Proxmox Wiki, to fix this you need to specify a serial port. This can be done by:

1. Navigating to your VM's configuration located in /etc/pve/qemu-server/[vmid].conf
2. Appending serial0: socket on a new line to the file
3. Restarting the VM

qm status 101
tatus: running

qm terminal 101
starting serial terminal on interface serial0 (press control-O to exit)
Debian GNU/Linux 8 debian8 ttyS0
debian8 login:

Add a virtual serial port to the VM
Provided your VM IS is 101

# open  /etc/pve/qemu-server/101.conf and add the following parameter at the end of file
serial0: socket

or use

qm set 101 -serial0 socket