Linux terminal, console, tty, pty, etc.

Title: concepts such as terminal, console, tty, and pty in Linux. Linux is a technology channel of the IT lab in China. Includes basic categories such as desktop applications, Linux system management, kernel research, embedded systems, and open source.

Basic concepts:

1> tty (collectively referred to as the terminal device ):

Tty is derived from Teletypes or teletypewriters. Originally, it refers to a telex typewriter, which reads and sends messages through a printer keyboard through a serial line. Later, it was replaced by a keyboard and a display, so now it is more appropriate to call the terminal.

A terminal is a type of terminal device. It has multiple types and generally uses tty for short.

2> pty (Pseudo Terminal, virtual terminal ):

But if we remotely telnet to the host or use xterm, do we still need a terminal to interact? Yes, this is the virtual terminal pty (pseudo-tty)

3> pts/ptmx (combining pts/ptmx to implement pty ):

Pts (pseudo-terminal slave) is the implementation method of pty. It is used with ptmx (pseudo-terminal master) to implement pty.

In the special file directory/dev/of a Linux system device, there are generally the following types of special device files on the terminal:

1. Serial Port Terminal (/dev/ttySn)

The Serial Port Terminal (Serial Port Terminal) is a Terminal device connected by a computer Serial Port. The computer regards each serial port as a character device. For some time, these serial port devices are usually called terminal devices, because at that time they were used to connect terminals. The device names corresponding to these serial ports are/dev/tts/0 (or/dev/ttyS0),/dev/tts/1 (or/dev/ttyS1), etc, the device numbers are (), (), and so on, respectively, corresponding to COM1 and COM2 in the DOS system. To send data to a port, You can redirect the standard output to these special file names on the command line. For example, if you type echo test>/dev/ttyS1 at the command line prompt, the word "test" is sent to the device connected to the ttyS1 (COM2) port.

2. Pseudo Terminal (/dev/pty /)

The Pseudo Terminal is a pair of logical Terminal devices (namely, the master and slave devices, and the operations on the master will be reflected on the slave ).

For example,/dev/ptyp3 and/dev/ttyp3 (or/dev/pty/m3 and/dev/pty/s3 in the device file system ). They are not directly related to physical devices. If a program regards ptyp3 (master device) as a serial port device, the read/write operations on the port are reflected in another ttyp3 (slave Device) corresponding to the logical terminal device. Ttyp3 is the logical device used by another program for read/write operations. Telnet host A communicates with the logon program of host A through A Pseudo Terminal.

3. control terminal (/dev/tty)

If the current process has a control Terminal (Controlling Terminal),/dev/tty is the device special file of the control Terminal of the current process. Can I use the command "ps? Ax to check which control terminal the process is connected. For the shell you log on to,/dev/tty is the terminal you are using, and the device number is (5, 0 ). Run the "tty" command to check which actual terminal device it corresponds. /Dev/tty is similar to a connection to the actually used terminal device.

4. console terminal (/dev/ttyn,/dev/console)

In Linux, a computer monitor is usually called a Console ). It simulates a Linux terminal (TERM = Linux), and some special files of the device are associated with it: tty0, tty1, tty2, and so on. When you log on to the console, tty1 is used. With Alt + [F1-F6] keys, we can switch to tty2, tty3 and so on. Tty1? Tty6 is called a virtual terminal, while tty0 is an alias of the virtual terminal currently in use. The information generated by the system will be sent to the terminal (also called a console terminal ). Therefore, no matter which virtual terminal is being used, the system information will be sent to the console terminal. /Dev/console refers to the console, which is a device that interacts with the operating system. The system directly outputs some information to the console. Currently, users can log on to the console only in single-user mode.

5 virtual terminal (/dev/pts/n)

A Pseudo Terminal in Xwindows mode. For example, if I use konsole in Kubuntu, It is a virtual terminal. Run the tty command to view/dev/pts/1.

6 Other Types

In Linux, there are many other types of special files on terminal devices for many different character devices. For example,/dev/ttyIn terminal devices for ISDN devices. I will not go into details here.

Tty devices include virtual consoles, serial ports, and Pseudo Terminal devices.

/Dev/tty indicates the current tty device. Input echo "hello">/dev/tty in the current terminal, which will be directly displayed on the current terminal.