/dev/ttyU0 (serial console) cannot get working

[jb82]

I have FreeBSD 14.1-RELEASE (host) and 15.0-CURRENT (guest) machines.

HW setup:
- Two USB => RS-232 cables connected in between with null-modem cable (3 cables in total).

On both machines I see the TTY: /dev/ttyU0 (please note the capital U).

On the guest.
In the default /dev/ttys there's only lower-cased version mentioned so I tweak that file with:

ttyU0   "/usr/libexec/getty std.115200" vt100   on secure

Not sure if connected, probably yes, but /var/log/messages shows tons of messages like:

getty[...]: open /dev/ttyu0: No such file or directory, sleeping 30 secs

(please, note the lower-case u)

On the host.
Now, I run cu -l /dev/cuaU0 -s 115200, it prints Connected but nothing happens since then.

Note. Cables should be fine, I hope, after playing with this for an hour and half I once get some login prompt from the guest (mentioning the hostname correctly) but it was not usable at all.

 

[Phishfry]

On FreeBSD the little U's are COM ports. The big U's are USB.

Example
/dev/cuau0 is serial port.
/dev/cuaU0 is USB port.

Same for tty ports.
/dev/ttyu0 is serial port
/dev/ttyU0 is USB port

 

[jb82]

On FreeBSD the little U's are COM ports. The big U's are USB.

Cool, thanks so much. First miracle resolved. But still.... It gets stuck even with 9600 baud:

jb@p1 ~> doas cu -l /dev/cuaU0 -s 9600
Connected


FreeBSD/amd64 (Amnesiac) (ttyU0)

login:

and server showed:

init[...]: getty repeating too quickly on port /dev/ttyU0, sleeping 30 secs

Crashing? Why?

 

[Phishfry]

Do you have both style cables to check? That's where I start when going equipment to equipment.
Null Modem and straight thru/crossover. Then start checking settings.

You are seeing a console but unable to type? You reverted your earlier setting right reboot needed?

 

[Phishfry]

I admire your security prose but you might want to mess with serial port using root them move to secure setting,
Maybe a permissions issue.

 

[Phishfry]

- Two USB => RS-232 cables

I totally missed that part.
So basically USB to USB. Same on both ends. Might require changes. to etc/ttys
Same deal is Null Modem Cable what is used between them?

There is a post on here to assist you with USB-USB. Many I bet.

 

[Phishfry]

My mentor covered it here:

Using USB > Serial adapter for console output

Hi all, I am trying to get a USB to serial adapter to be the tty used for console output. The driver works fine and I get a /dev/ttyU0 device. Is it possible to use this connection for the default console output for the machine? Thanks!

forums.freebsd.org

More insight:

headless console USB-to-USB

Hi all, I use an HP Pavilion laptop without screen (torn off) as a headless home server. I access it either on the console, plugging in an external VGA monitor, or via ssh. Lately I got locked out because: 1. i915kms was deprecated and blacklisted in /boot/loader.conf, 2. I messed up with...

forums.freebsd.org

Connect Via USB Cable

I have been reading through Chapters 26 and 27 on serial connections. I must be missing something. I'll ask what seems like a very basic question. Can I connect one FreeBSD computer to another via a USB ports and a plain jane USB cable and obtain shell access? Do I need a special adapter or a...

forums.freebsd.org

 

[jb82]

My mentor covered it here:

Using USB > Serial adapter for console output

Hi all, I am trying to get a USB to serial adapter to be the tty used for console output. The driver works fine and I get a /dev/ttyU0 device. Is it possible to use this connection for the default console output for the machine? Thanks!

forums.freebsd.org

More insight:

headless console USB-to-USB

Hi all, I use an HP Pavilion laptop without screen (torn off) as a headless home server. I access it either on the console, plugging in an external VGA monitor, or via ssh. Lately I got locked out because: 1. i915kms was deprecated and blacklisted in /boot/loader.conf, 2. I messed up with...

forums.freebsd.org

Connect Via USB Cable

I have been reading through Chapters 26 and 27 on serial connections. I must be missing something. I'll ask what seems like a very basic question. Can I connect one FreeBSD computer to another via a USB ports and a plain jane USB cable and obtain shell access? Do I need a special adapter or a...

forums.freebsd.org

Will check those, thanks!

 

[jb82]

My mentor covered it here:
...

Read most of those, only a partial luck so far. Guest's loader.conf shows:

boot_multicons="YES"
boot_serial="YES"
comconsole_speed="115200"
console="comconsole,efi"

I have partial success but it's not responsive:

# cu -s 115200 -l /dev/cuaU0
Connected

FreeBSD/amd64 (Amnesiac) (ttyU0)

login:

also

root@:~ # cat /etc/ttys | grep U0
ttyU0   "/usr/libexec/getty std.115200" vt100   on secure

Two USB/RS-232 converters are Serial Bridge Prolific Technology, Inc. which are wildly used in those previous threads. No idea, what else might be wrong...

 

[covacat]

try
"/usr/libexec/getty 3wire instead of std

 

[jb82]

try
"/usr/libexec/getty 3wire instead of std

Sometimes water can even flow uphill. Sometimes, miracles simply happen. After switching to 3wire and using 9600 baud, everything works perfectly. I had no idea that those two cables were 3wire. Now, it's time to study what 3wire actually is.

The only downside is, that I cannot get anything besides 9600 baud rate. But that's fine for my use case.

Splendid! Thank you, guys. This forum makes FreeBSD even better.

 

[covacat]

these cables only have rx tx and ground no cts/rts and dcd