Serial port between two VMs?

[Tom Moyer]

Is it possible to connect the serial ports of two virtual machines on Proxmox? I am working on a project that requires me to debug the kernel over a serial cable. I see a lot of documentation on connecting the physical host to a guest via serial but I need specifically guest to guest serial connections.

 

[Stefan_R]

PVE (and even QEMU itself AFAIK) doesn't directly support it, but you can emulate it by creating a serial connection to the host for both VMs and then connecting them together via socat.

E.g., assuming your VMs have ID 101 and 102:

# add the serial ports
qm set 101 -serial0 socket
qm set 102 -serial0 socket

# start both VMs
qm start 101
qm start 102

# connect the two serial ports on the host
socat UNIX-CLIENT:/var/run/qemu-server/101.serial0 UNIX-CLIENT:/var/run/qemu-server/102.serial0

You can test the connection by simply echo-ing some text into /dev/ttyS0 on one VM while cat-ing /dev/ttyS0 on the other. Keep in mind that socat has to keep running on the host, lest the VMs will be disconnected.