Linux endpoint concept, pseudo terminal, serial terminal, virtual terminal, console

Historical origins of the terminal

The initial computer is expensive, so a computer is generally used by multiple people at the same time. In this case, a computer needs to connect many sets of keyboards and monitors for more than one person to use. In the past, there is a device that can connect to a computer, only a monitor and keyboard, and a simple processing circuit, which itself does not have the ability to process computer information, he is responsible for connecting to a normal computer (usually through the serial port), then log on to the computer and operate on the computer. Of course, the computer operating system at that time is multi-tasking multi-user operating system. A device that only displays and keyboards can be connected to a computer via a serial port is called a terminal.

And what about the console? In the computer, the keyboard and the monitor connected directly to the computer are called consoles. Please note the difference between it and the terminal, the terminal is connected through the serial port, not the computer itself has some equipment, and the console is the computer itself has a device, a computer has only one console. When the computer starts, all information is displayed to the console, not to the terminal. In other words, the console is the basic device of the computer, and the terminal is an additional device. Of course, because the console also has the same function as the terminal, the console is sometimes blurred to collectively known as the terminal. In the computer operating system, information unrelated to the terminal, such as kernel messages and background service messages, can be displayed on the console, but will not appear on the terminal.

Now that computer hardware is getting cheaper and more expensive, it's usually a person who has a computer that is super-done, and no longer connects to the "end-device" in the real sense of the past, so the concept of terminals and consoles has evolved slowly. Terminals and consoles evolved from the concept of hardware into the concept of software. Now the terminal, such as the virtual terminal in Linux, is the concept of software, he uses the computer software to simulate the way the previous hardware. For example, in Linux, you can switch six virtual terminals with ALT+F1 ~ F6, which is the reason why this is called "Virtual terminal", as it is the six terminal equipment in the computer which was used by many people. Of course, today's Linux can also be connected to a real terminal via a serial line.

1. Pseudo Terminal

The pseudo terminal is also called the analog terminal, the terminal interface which is opened on the remote connection terminal or the graphical interface.

2. Virtual Terminal

CTRL+ALT+F[1-6]

Graphics Terminal Ctrl+alt+f7

3. Physical terminal (console)

directly connected to the host (Console interface connected)

4. Serial Terminal

Serial output

The system starts normally, displays the boot process information output to the physical terminal, when the physical terminal is initialized by the system, called the Virtual terminal (graphical interface or ctrl+alt+f[1-6]) to open the graphical interface to simulate a command window is a pseudo terminal, or remotely login to the system, the terminal is also a pseudo terminal

The difference between the current system is that terminal

Use the command TTY, which represents the device file for the current terminal, (the following # indicates a number)

1, the result shows:/dev/pts/# represents pseudo terminal

2, the result shows:/dev/tty# represents the Virtual terminal

3, the result shows:/dev/console represents the physical terminal (console)

4, the result shows:/dev/ttys# means serial terminal

The same user login system, corresponding to different systems/devices, belong to different processes of users, there are devices have the corresponding device files.

Command: Who views all users logged into the system and their information.

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Linux endpoint concept, pseudo terminal, serial terminal, virtual terminal, console