Linux Keyboard – How to Swap Keys in a Virtual Terminal

Partial answer (because it's just an outline, and untested):

Write a demon which listens to whatever /dev/input device corresponds to your main keyboard (there are symlinks, look at them). Start that demon as the user you specify, using whatever init system you have (systemd, sysv, whatever).

The demon processes key events as defined in input-events-codes.h (or look at the source code of evtest). It has a state machine that recognizes your desired key sequences, and spawns whatever process you specify when such a sequence is complete.

This should be available before you login, and will always execute as the same user, no matter what user you are logged in at the virtual console. It will also execute under X, again as the same user.

Alternative, if you want to execute something in a shell: Use tmux or a similar program which can bind key sequences to actions. I suppose it should also be possible to automatically start tmux and attach to a new session whenever you log in at a virtual console, but I haven't looked into that.

This won't work before log in, but will also work in graphical terminal emulators that have keyboard focus, and will execute the script as the user which is logged in.

Firstly, this question was asked on Retrocomputing, but the community found it more suitable for this site. But I got an answer in the comment section, so copy it here:

The Linux virtual console emulates a (sort of) VT102 terminal in ON-LINE mode connected to a Linux (serial) tty device. The Linux tty driver doesn't normally echo back the escape control character, and instead echos ^[. If you don't want the tty driver to do this, then use stty -ctlecho. Also real VT102 terminals don't support colour, it works with the Linux virtual console anyways because its not really VT102 compatible.

I have tried the stty -ctlecho and it works almost as expected - only one subquestion - is the real VT102 also wasn't displaying characters after person press ESC and start type escape sequence, so the person were type it in the blind manner?