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Chapter 2: Terminal

Early Terminals

ibm-2260

Early terminals were standalone hardware devices used to connect to main computers or servers. They typically included:

  • Input Device: such as a keyboard, used for inputting commands and data.
  • Output Device: such as a display or printer, used for displaying calculation results and system feedback.

Examples: early Teletype (tty) terminals, DEC VT100 terminals.

Modern Terminals

iterm2

Modern terminals exist more in software form, i.e., terminal emulators, running as applications in modern operating systems (such as Linux, macOS, Windows), simulating the functions of early hardware terminals.

Terminal Emulators

TerminalDescription
iTerm2Advanced terminal emulator on macOS systems, offering rich features like split screens, tabs, and search.
GNOME TerminalDefault terminal emulator commonly found on Linux systems, powerful and easy to use.
PuTTYWidely used SSH client on Windows systems, suitable for remote connections and management.
Windows TerminalModern terminal emulator on Windows systems, supporting multiple command-line environments like PowerShell, CMD, WSL.

Teletype

teletype-model-33

Although Teletype devices are no longer in use, their concept and functionality are still preserved in Linux.

/dev/tty

You can see its file type is c (character device), representing the terminal device connected to the current process.

ls -l /dev/tty
crw-rw-rw- 1 root tty 5, 0 Aug  7 22:33 /dev/tty

Its permission is 666, major device number is 5, minor device number is 0, which is what we commonly see as standard input/output.

echo "Hello, World" > /dev/tty
read -p "Enter your name: " name < /dev/tty
echo "Hello, $name"

/dev/pts

PTS stands for Pseudo-Terminal, /dev/pts is a directory for storing pseudo-terminal device files.

ls -l /dev/pts/
crw------- 1 root tty  136, 0 Aug  8 09:52 0
c--------- 1 root root   5, 2 Aug  7 21:30 ptmx

Listing the files in the /dev/pts directory, you will generally see two types of files.

  • ptmx: Master Device, used for creating and managing pseudo-terminal pairs.
  • 0/1/2: Slave Device, each corresponding to a number for an ssh session.

Entering the tty command in the command line can show the pseudo-terminal device file currently connected.

tty
/dev/pts/0
man tty
tty - print the file name of the terminal connected to standard input

Get Logged-in User

The most common method is the w command.

w
 11:18:19 up 15 days, 20:08,  2 users,  load average: 0.00, 0.01, 0.05
USER     TTY      FROM             LOGIN@   IDLE   JCPU   PCPU WHAT
root     pts/0    120.231.138.130  10:59    3.00s  0.02s  0.00s w
root     pts/1    120.231.138.130  11:11    6:41   0.01s  0.01s -bash

You can also use the who command.

who
root     pts/0        2024-08-04 10:59 (120.231.138.130)
root     pts/1        2024-08-04 11:11 (120.231.138.130)

Of course, you can directly use ls as well.

ls -l /dev/pts/
crw------- 1 root tty  136, 0 Aug  8  2024 0
crw------- 1 root tty  136, 1 Aug  8 09:53 1
c--------- 1 root root   5, 2 Aug  7 21:30 ptmx

Send Msg to PTS

echo "hello, world" > /dev/pts/1

Kill a PTS

ps -t /dev/pts/1
kill -9 PID
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Chapter 1: Say My Name
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