Using 2020-12-02-raspios-buster-armhf-lite I have attached a USB to serial cable and enabled logins with
sudo systemctl enable serial-getty@ttyUSB0.service sudo systemctl start serial-getty@ttyUSB0.service
This works fine. I can attach the serial cable to a PC and login. However if I disconnect the USB cable from the Raspberry Pi then reconnect it, I can no logger get a login prompt. Or if I boot the Pi without the USB cable attached I can't get a login prompt after plugging it in. It seems the USB cable has to be attached at boot time. Is there anyway to "hot plug" the USB cable and get a login prompt?
My goal is to have a totally headless Pi (with no networking) where if I need to login I can attach a USB to serial cable and get a login prompt.