There is some software package that allow run plug a tmux console into a null modem device (/dev/nmdm)?

Now that's just paranoia. If you have sensible settings for SSH, you'll be fine. Not to mention that realistically speaking, your VM is most likely not even visible to port scanners on the Internet, and you don't present an attractive target for anyone capable of launching an attack that does any real damage. I have a few devices with SSH access sitting behind a 192.168.1.1/24 network, tell me if you can see them.

Well, we're IPv6 nowadays, and NAT protection doesn't hold anymore. I think it is valid to by default consider a networked entity to be a potential attack surface.

Concerning the topic: I am using cu inside tmux.
 
IPv6 nowadays
Surprisingly, not everyone has the ability to get Internet-legal, routable IPv6 addresses, not without a tunnel to a service provider like Hurricane Electric... I've seen comments on these Forums that some people are 'still stuck with a tunnel provider'.

I'm on US West Coast, and my market still doesn't have a handle on IPv6, in spite of claims that 'IPv6 is supported'. Maybe technically possible, but certainly not routed from private devices yet.
 
The same executable can have different behavior depending on argv[0] value (the name under which it was executed).
E.g., rm(1) and unlink(1).
Code:
$ ls -i -1 /bin/rm /bin/unlink
3479 /bin/rm
3479 /bin/unlink
(no need to use diff or cmp, even)
They look like a hard link
Code:
$ ls -i -1 /usr/bin/cu /usr/bin/tip
5032 /usr/bin/cu
5032 /usr/bin/tip
[code]
 
Surprisingly, not everyone has the ability to get Internet-legal, routable IPv6 addresses, not without a tunnel to a service provider like Hurricane Electric... I've seen comments on these Forums that some people are 'still stuck with a tunnel provider'.
I am indeed using HE, there is not much problem with that - they even delegate the reverse-DNS to my own nameservers.

I'm on US West Coast, and my market still doesn't have a handle on IPv6, in spite of claims that 'IPv6 is supported'. Maybe technically possible, but certainly not routed from private devices yet.
That is everywhere. Businesses are reluctant to go IPv6, for unknown reasons (maybe lack of skill). But if you have a business, you can choose your uplink, and if you are private site, tunnels are not such bad.
 
cu(1) and tip(1) which (I believe) are in base.
I cannot run tip(1) from ssh, thus it is useless.
Yes, they are. cu is my favorite, very simple and does not require any configuration file.
For the other part cu(1) does work, but all the shell functionality is totally broken, cannot edit lines (move the cursor) and use TUI or anything.
As much as I love tmux(1) this setting is fairly annoying. Alternatively you could run cu(1) in tmux and connect that to the serial console of the VM. Or simply fire off vm console <myvm> in a tmux window.
And have tried cu(1), and it gives a serial console, but the serial console is broken, cannot use TUI or edit lines (move the cursor).
How about minicom?
Just tried minicom, it works but looks like also has the same problems of cu(1), maybe I have no configured any of them well.
 
I cannot run tip(1) from ssh, thus it is useless.
I do it fairly often. Not sure why you can't get it to play ball. Any specific error messages?
Try ssh -> tmux -> tip.

For the other part cu(1) does work, but all the shell functionality is totally broken, cannot edit lines (move the cursor) and use TUI or anything.
This is because serial terminals are more limited as per the standard.

As mentioned above, perhaps use the serial purely as a transport for TCP/IP (aka PPP) and then use ssh through that.
 
I do it fairly often. Not sure why you can't get it to play ball. Any specific error messages?
Try ssh -> tmux -> tip.
Probably will work, but with that level of indirection, how many escape sequences will be there?.
The error message was "missing interactive session".
This is because serial terminals are more limited as per the standard.
It is not possible to configure it to speak vt100?.
Also grub does not even respond to the arrow key when doing for the null modem setup, but does respond to the arrow keys, when the serial console is connected to stdio.
 
Probably will work, but with that level of indirection, how many escape sequences will be there?.
The tmux escape sequence is quite different so doesn't count. But yep, the i.e ~~. may be more awkward for ssh+tip.
The error message was "missing interactive session".

It is not possible to configure it to speak vt100?.
Also grub does not even respond to the arrow key
Interesting. What is the TERM env variable at any of these points? (minus grub perhaps).
 
The tmux escape sequence is quite different so doesn't count. But yep, the i.e ~~. may be more awkward for ssh+tip.

Interesting. What is the TERM env variable at any of these points? (minus grub perhaps).
First we start with xterm-256color at a row session of Konsole, then I enter with ssh to the machine, ssh my-user@my-machine 'echo $TERM',and get nothing. And finally when entering in the debian-12-nocloud-amd64.img with bhyve, I got vt220.
 
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