USB TTY Serial Login

Many Generic x86 Boards and Appliances provide a DB9-RS232 serial port for console access, and since modern PC's / Notebooks / Chromebooks do not have a serial port, a USB-to-Serial cable adapter must be used. You probably already knew that.

What is new is the ability to connect a second USB-to-Serial cable adapter (USB-to-Serial ↔ Serial-to-USB) to a USB port on your AstLinux box and automatically spawn getty to establish a login. This is particularly useful for Generic x86 Boards and Appliances that only have a VGA video console, or to establish one or more serial logins in addition to a serial console. The USB TTY serial baudrate and terminal type can be specified independently from the system console configuration.

Note: AstLinux 1.2.10 or later is required

Configuration:

Enable this feature by setting USBTTY to yes:

/mnt/kd/rc.conf.d/user.conf

USBTTY="yes"

The default baud rate is 115200, you may specify a different baud rate (for example):

USBTTY_BAUD_RATE="19200"

The default terminal type is vt100, you may specify a different terminal type (for example):

USBTTY_TERM_TYPE="xterm-color"

Equipment:

It is recommended to use a USB-to-Serial adapter containing a FTDI chipset, which is supported in AstLinux and is built-in to most modern OS's including Chromebooks. The older PL2303 Prolific Chipset adapter will also work if you already have one.

The two USB-to-Serial adapters are connected together with a DB9 Null Modem cable or mini adapter. A crossover connection, not straight through.

To be clear, the back-to-back USB-to-Serial adapters do not have to use the same chipset or brand, as long as internal driver support exists for each USB end, respectively.

Operation:

Join the two USB-to-Serial adapters together using a DB9 Null Modem cable or adapter.

Plug one USB connector into your PC / Notebook / Chromebook, start a terminal emulator (screen, minicom, etc.) at 115200 baud (unless changed).

Tip -> screen /dev/ttyUSB0 115200

Tip -> minicom -D /dev/ttyUSB0 -b 115200

Plug the other USB connector into your AstLinux box. You should immediately see a login prompt on your terminal emulator screen.

Photos:

USB 2.0 to RS232 DB9 Serial Cable Male A Converter Adapter with FTDI Chipset
https://www.amazon.com/dp/B00QUZY4L0/

DB9 Female / DB9 Female Null Modem Mini Adapter
https://www.amazon.com/dp/7507825604/