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I checked this thread: What is the exact difference between a 'terminal', a 'shell', a 'tty' and a 'console'?

However, I don't understand in practice how to connect directly to the lower system layers like "terminal".

Is it possible or is "terminal" densely bound with "shell" and it is like a monolith?

Edited: What I mean is the Linux terminal tty. For example, I can assess the grub terminal during a system boot by clicking Ctrl-c.

  1. How to access Linux terminal during a boot?

  2. Is it possible to access the Linux terminal directly while Linux is running without using any shell? Are there any shortcuts or something?

  3. Is tty and xterm the same thing?

t7e
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    Yes, you can connect directly to a terminal, eg. with fd = open("/dev/ttyS0", O_RDWR) from C. You don't need any shell. Or do you mean how to connect to a terminal from a shell, but without using a shell ;-) ? Your Q is too broad to be useful IMHO. –  Mar 07 '20 at 08:27
  • I don't quite understand how it works and, probably, therefore my question is not precise. What I mean is the Linux terminal tty. For example, I can assess the grub terminal during a system boot by clicking Ctrl-c. How to access Linux terminal during a boot? Is it possible to access it while Linux is running? – t7e Mar 07 '20 at 08:38
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    There isn't a single Linux terminal. If you mean the first virtual terminal (/dev/tty1), it's probably via Ctrl-Alt-F1. It has nothing to do with the grub "terminal" -- that is simply a command line interface of grub, which disappears as soon as grub has started Linux or another OS. –  Mar 07 '20 at 08:40
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    And please add any clarifications to your Q; nobody reads the comments ;-) –  Mar 07 '20 at 08:44

1 Answers1

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Is it possible to connect directly to the “terminal” in Linux without using “shell”?

If you're looking at this from the user's point of view, I'd say the assumptions in the above are backwards. You, as the user, don't really connect to a terminal with the shell, you connect to the shell via the terminal.

Remember, the terminal is this, a device with a screen, a keyboard and a cable connecting it to your computer:

enter image description here

From the programmer's point of view, the shell connects to the terminal to be able to read and write what the user enters. It doesn't have to be shell though, any program could open one of the /dev/ttywhatever files. Or get launched by the shell and inherit a file handle to one: if you run cat from the shell, the cat process connects to the terminal.

Of course, in practice, you probably don't have a terminal that looks like that, but a software that emulates it. Something like xterm or the kernel's text-mode virtual console. Or you could take a laptop, connect it via a serial cable and run minicom on it, and use it pretty much like a serial terminal.

For example, I can assess the grub terminal during a system boot by clicking Ctrl-c.

How to access Linux terminal during a boot?

Is it possible to access the Linux terminal directly while Linux is running without using any shell? Are there any shortcuts or something?

Linux really doesn't have a built-in command line interface like grub does. That's what the various shell programs are for...

You might be able to access (to type in characters on) a serial console or virtual console with no program connected to it, but it wouldn't be very useful. You'd have no-one to talk to.

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