I am running fedora vm under XP host and using NAT connection to the Internet. It usually works fine, but some time the connection is just lost. I went menu System->Admin->Network and see the interface eth0, but I cannot activate or deactivate. The status is inactive. (when the connect works, the status is active). so I try "ifdown eth0" and "ifup eth0" command, and got

"Error: Connection activation failed: Device not managed by NetowrkManger

The menu System->Admin->Network device control show no interface.

I am not sure what happened.

which VM software are you using ?

i fix it. i had to add managed=true in one of the file (i don't remember) i found the instruction from the Internet. It is Fedora.