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In the Linux operating system, TTY (Teletypewriter) and PTS (Pseudo Terminal Slave) are two different types of terminals. They each have different uses and characteristics, which are crucial for understanding the user interface of Linux and how to perform operations such as remote login.
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Definition and History
tty is an abstraction of physical or virtual terminals, originating from early teletypes. In modern Linux, each physical terminal or virtual console (such as the interfaces switched by Ctrl+Alt+F1~F6) corresponds to a tty device.
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Device Files
Device files are located at /dev/ttyN (e.g., /dev/tty1), or virtual terminals like /dev/ttyS0 (serial terminals).
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Usage Scenarios
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Physical console (directly connected keyboard and monitor). -
Virtual terminals switched by Ctrl+Alt+Fn. -
Serial terminals (e.g., debugging embedded devices).
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Characteristics
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Direct interaction with the kernel, no need for network protocols. -
Strict permission control (e.g., /etc/securetty can restrict root login to tty devices).
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Definition and Use
pts is the slave side of a pseudo-terminal, used to simulate terminal behavior. It usually appears in pairs with ptmx (the master device of the pseudo-terminal), created by terminal emulators (like SSH, graphical terminal).
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Device Files
Dynamic device files are located at /dev/pts/N (e.g., /dev/pts/0), with each session assigned a unique number.
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Usage Scenarios
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SSH remote login. -
Terminal emulators in graphical interfaces (like GNOME Terminal, Konsole). -
Session multiplexing with screen or tmux.
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Characteristics
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Data forwarding through the master-slave device pair (ptmx and pts). -
Supports network transmission (e.g., SSH encrypted communication). -
User permissions are more flexible (depending on the user of the initiating process).
|
Feature |
tty |
pts |
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Device Type |
Physical terminal or virtual console |
Pseudo-terminal (network/simulated terminal) |
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Device Path |
/dev/ttyN or /dev/ttySN |
/dev/pts/N |
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Creation Method |
Pre-allocated at system startup |
Created dynamically (on demand) |
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Dependency |
Direct connection or virtual console |
Requires master device (ptmx) to cooperate |
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Typical Applications |
Local console, serial devices |
SSH, graphical terminals, terminal multiplexing |
# View current terminal device file path
$ tty
/dev/pts/0 # If it is a pseudo-terminal, it shows pts; if it is a physical terminal, it shows ttyN$ ps -p $$ # View terminal information of the current Shell1. Master-Slave Device Creation
When a user logs in via SSH or a graphical terminal, the terminal emulator (like sshd) creates a pair of pseudo-terminals:
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Master Device (ptmx): Controlled by the terminal emulator, responsible for receiving user input. -
Slave Device (pts): Associated with the user’s Shell process, receiving content forwarded from the master device.
2. Data Flow
User Input → Master Device (ptmx) → Slave Device (pts) → Shell Process
Shell Output → Slave Device (pts) → Master Device (ptmx) → Terminal Display
SSH simulates terminal behavior through pseudo-terminals, so the session is associated with /dev/pts/N.
Edit the /etc/securetty file (only list allowed tty devices, excluding pts).
tty devices typically belong to root:tty, while pts devices belong to the user who started them.
tty: Directly associated with hardware or virtual consoles, suitable for local operations.
pts: Simulated through pseudo-terminals, used in remote or graphical environments, offering greater flexibility.
Understanding the differences between the two helps in troubleshooting terminal permissions, session management issues (e.g., SSH configuration or /dev device permission errors).
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