What does tty mean in centos

In centos, tty is the abbreviation of "Teletype" and is the collective name for terminal equipment; Teletype is the earliest terminal equipment produced by Teletype Company. It is a character-type device and has many types. , the device name is placed in the special file directory "/dev/".

The operating environment of this article: centos 6.4 system, Dell G3 computer.

What does tty mean in centos

The terminal is a character-type device, which comes in many types. tty is usually used to refer to various types of terminal devices.

tty is the abbreviation of Teletype. Teletype was one of the earliest terminal devices, much like a teletypewriter (or ), and was produced by the Teletype Company. The device name is placed in the special file directory /dev/. The terminal special device files generally include the following types:

1. Serial port terminal (/dev/ttySn)

Serial Port Terminal is a terminal device connected using a computer serial port. The computer treats each serial port as a character device. There was a time when these serial port devices were often called terminal devices because their primary use at that time was for connecting to terminals. The device names corresponding to these serial ports are /dev/tts/0 (or /dev/ttyS0), /dev/tts/1 (or /dev /ttyS1), etc., and the device numbers are (4,0), ( 4,1), etc., respectively corresponding to COM1, COM2, etc. under the DOS system. To send data to a port, you can redirect standard output to these special file names on the command line. For example, typing at the command line prompt: echo test > /dev/ttyS1 will send the word "test" to the device connected to the ttyS1 (COM2) port.

2. Pseudo terminal (/dev/pty/)

Pseudo Terminal (Pseudo Terminal) is a pair of logical terminal devices, such as /dev/ptyp3 and / dev/ttyp3 (or /dev/pty/m3 and /dev/pty/s3 respectively in the device file system). They are not directly related to actual physical devices. If a program sees ttyp3 as a serial port device, its read/write operations on that port will be reflected on the other end of the logical terminal device pair (ttyp3). ttyp3 is a logical device used by another program for read and write operations. In this way, two programs can communicate with each other through this logical device, and one of the programs using ttyp3 thinks it is communicating with a serial port. This is much like a pipe operation between pairs of logical devices.

For ttyp3 (s3), any program designed to use a serial port device can use this logical device. But for programs that use ptyp3, they need to be specially designed to use ptyp3 (m3) logical devices.

For example, if someone uses the telnet program to connect to your computer on the Internet, the telnet program may start connecting to the device ptyp2 (m2) (a pseudo terminal port). At this time, a getty program should be running on the corresponding ttyp2 (s2) port. When telnet obtains a character from the remote end, the character will be passed to the getty program through m2 and s2, and the getty program will return the "login:" string information to the network through s2, m2 and the telnet program. In this way, the login program and the telnet program communicate through the "pseudo terminal". By using appropriate software, it is possible to connect two or even more pseudo-terminal devices to the same physical serial port.

Before using the device file system (device filesystem), in order to obtain a large number of pseudo-terminal device special files, HP-UX AIX and others used a more complex file naming method.

3. Control terminal (/dev/tty)

If the current process has a controlling terminal (Controlling Terminal), then /dev/tty is the current process Device special files that control the terminal. You can use the command "ps -ax" to see which control terminal the process is connected to. For the shell you log in to, /dev/tty is the terminal you use, and the device number is (5,0). Use the command "tty" to see which actual terminal device it corresponds to. /dev/tty is somewhat similar to a connection to the actual terminal device used.

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

In UNIX systems, the computer monitor is usually called the console terminal (Console ). It emulates a terminal of type Linux (TERM=Linux), and has some device special files associated with it: tty0, tty1, tty2, etc. When you log in at the console, tty1 is used. When using the Alt [F1-F6] key combination, we can switch to tty2, tty3, etc. tty1 – tty6 and so on are called virtual terminals, and tty0 is an alias of the currently used virtual terminal, and the information generated by the system will be sent to this terminal. Therefore, no matter which virtual terminal is currently being used, system information will be sent to the console terminal.

You can log in to different virtual terminals, so the system can have several different sessions at the same time. Only the system or super user root can write to /dev/tty0,

5. Other types

There are also many other types of terminal device special files for many different character devices. For example, /dev/ttyIn terminal device for ISDN equipment, etc.

Recommended tutorial: "centos tutorial"

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