First I would recommend snuggling up with your Soekris manual ¹ by the fire and getting out your corn cob pipe.

Setting up console access:

The Soekris wiki provides some guidance ² to get you started, but it does assume that you have an idea how to do this. I was a bit ignorant to the whole serial cable ³ vs null modem ⁴ cable. Picked up a usb to serial cable off eBay for $3, it has USB and DB9 male connections, so it is the wrong type of cable and the wrong connector, go figure. Turns out that is not so bad after some searching the internet, decided I would take a crack at creating a Null Modem adapter. Went down to my neighborhood Radio Shack and picked up two female DB9 connectors and used some useful wiring diagrams online to create a simple null modem with no handshaking ⁵.

With a cable we are ready to validate that we can connect, being that my only experience with console access was RS232 programming in college, I was looking for some quick starts to get me going and found a useful article on connecting to Soekris from minicom ⁶ on UnixCraft. Once I plugin the cable I can tail the dmesg output for where my device is located, in this case ttyUBS0

[14635.254804] usb 1-1.5.1.3: new full speed USB device using ehci_hcd and address 15
[14635.427194] usbcore: registered new interface driver usbserial
[14635.427214] USB Serial support registered for generic
[14635.427283] usbcore: registered new interface driver usbserial_generic
[14635.427285] usbserial: USB Serial Driver core
[14635.434341] USB Serial support registered for ch341-uart
[14635.434385] ch341 1-1.5.1.3:1.0: ch341-uart converter detected
[14635.436030] usb 1-1.5.1.3: ch341-uart converter now attached to ttyUSB0
[14635.436048] usbcore: registered new interface driver ch341

Start up minicom and configure your console before you turn on your Soekris device, I am working from Ubuntu so I need to sudo to get access to the ttys sudo minicom -s then navigate to the Serial Port setup screen.

Showing setup and some samples of it working.

Now I just need to install an OS and do something useful with this box ;)

Update: I also tried via cu to see if that was any easier to use, but they both get you to the same place, only thing I found was that I needed to add permissions to /dev/ttyUSB0 before I could connect.

sgw@geb:~$ sudo cu -e -o -s 19200 -l /dev/ttyUSB0
cu: open (/dev/ttyUSB0): Permission denied
cu: ttyUSB0: Line in use
sgw@geb:~$ sudo chmod 666 /dev/ttyUSB0
[sudo] password for sgw:
sgw@geb:~$ sudo cu -e -o -s 19200 -l /dev/ttyUSB0
...

Reference: