I have an Ubuntu 23.10 system with agetty running on its eight serial ports. I can hook up most terminals to the ports and login to a bash shell.

When I try to use a Teletype ASR 33, however, I get the login prompt and I answer enter the username. If I hit Return, nothing happens. If I hot Line Feed, the Password prompt is shown.

After I enter the password (all uppercase) Incorrect password is shown.

Since the prompts are displayed properly, I’m pretty sure the baud rate, BPS and stop bits are correct. What else can I check?

I start agetty this way:

agetty  -L -U ttyUSB0 110 tty

The -L means it’s a dedicated line, not dial-in. The -U means the terminal is uppercase only and some upper/lowercase conversions should be made.

The port is a USB to serial port (ttyUSB0), baud is 110.