You remember my Openbsd router ? It’s an APU from Pc Engines. When you plug those machines under Linux, you get a connection on /dev/ttyUSB0. But under OpenBSD ?

NB : Yes, not easy to follow. I want to connect to my OpenBSD router from another OpenBSD machine. What’s happening ?

Well, you get to connect to /dev/cuaU0.


Actually, you can make your life easier writing the connection’s details in the remote file :


See, you have the driver (/dev/cuaU0) and its bauds speed.

And now I can do that (connection with cu on the host mirror) :

stephane@blackblock:/home/stephane doas cu mirror
doas ( password: 
Connected to /dev/cuaU0 (speed 115200)

OpenBSD/amd64 ( (tty00)


I copied that on my two OpenBSD machines : blackblock, the server, and bandersnatch, the laptop. So I can connect easily from those two without having to remember the parameters.


I permanently plugged the serial cable between my server and the router (both running OpenBSD). Now I don’t need anymore to plug or unplug the router when I need to take direct control of the router (during upgrades or router’s crashes, which are rare).

If I need to quickly take control, I just need to ssh on the server (blackblock), and from there, serial connection through cu. But I cannot disconnect from cu through ssh. I can only properly disconnect from cu when I am working from bandersnatch.

To disconnect, I shall use ~. and that does not work through ssh but only on bandersnatch.