历史
- 1830s年代，出现了电报，后面出现发送电报使用的teleprinter (teletypewriter, teletype or TTY)，用来发送和接手信息。
- 1950s年代，大型机出现，只有console操作面板(没有键盘、没有显示器)
图片来源 - 1960s年代，小型机出现
- 使用teletypewriter作为大型机和小型机的输入、输出设备
- 使用物理线缆连接TTY和机器的物理插口
- 给机器的系统写一个驱动器(driver，这里留意一下这个TTY driver)
- 微型机的出现，键盘、服务器的出现，不在需要TTY。操作系统在内核中，写了一个terminal emulator。不再使用TTY这样的物理设备。
- 终端模拟软件
- VT100 VT220 XTerm等
- 现在常用ssh登录到一台远程服务器上。pseudo terminal的出现
- pseudo terminal分为2部分，master部分(ptmx)，slave部分(pts/0,pts/1)
定义
console
最开始的大型机、小型机，机器上有自有的控制台 a flat board that contains the controls for a machine, piece of electrical equipment, computer etc 机器、电器设备、电脑的控制台、操作台
图片来源
tty
+----------+ Physical Line +----------+
| teletype |<--------------------->| teletype |
+----------+ +----------+
tty本身就是一种终端，teletypewriter。 一种特定的设备文件(一切皆是文件)，基本和terminal相同的意思。tty是计算机系统操作的文件,terminal是文件另一端的设备。 内核提供一些针对键盘、显示器这样的tty。另一些是伪tty,有仿真终端程序提供。
tty 子系统
+-----------------------------------------------+
| Kernel |
| +--------+ |
| +--------+ +------------+ | | | +----------------+
| | UART | | Line | | TTY |<---------->| User process A |
<------>| |<->| |<->| | | +----------------+
| | driver | | discipline | | driver |<---------->| User process B |
| +--------+ +------------+ | | | +----------------+
| +--------+ |
| |
+-----------------------------------------------+
TTY设备
+----------------+
| TTY Driver |
| |
| +-------+ | +----------------+
+------------+ | | |<---------->| User process A |
| Terminal A |<--------->| ttyS0 | | +----------------+
+------------+ | | |<---------->| User process B |
| +-------+ | +----------------+
| |
| +-------+ | +----------------+
+------------+ | | |<---------->| User process C |
| Terminal B |<--------->| ttyS1 | | +----------------+
+------------+ | | |<---------->| User process D |
| +-------+ | +----------------+
| |
+----------------+
键盘显示器连接
使用 Terminal Emulator
+-----------------------------------------+
| Kernel |
| +--------+ | +----------------+
+----------+ | +-------------------+ | tty1 |<---------->| User processes |
| Keyboard |--------->| | +--------+ | +----------------+
+----------+ | | Terminal Emulator |<->| tty2 |<---------->| User processes |
| Monitor |<---------| | +--------+ | +----------------+
+----------+ | +-------------------+ | tty3 |<---------->| User processes |
| +--------+ | +----------------+
| |
+-----------------------------------------+
SSH连接方式
+----------+ +------------+
| Keyboard |------>| |
+----------+ | Terminal |
| Monitor |<------| |
+----------+ +------------+
|
| ssh protocol
|
↓
+------------+
| |
| ssh server |--------------------------+
| | fork |
+------------+ |
| ↑ |
| | |
write | | read |
| | |
+-----|---|-------------------+ |
| | | | ↓
| ↓ | +-------+ | +-------+
| +--------+ | pts/0 |<---------->| shell |
| | | +-------+ | +-------+
| | ptmx |<->| pts/1 |<---------->| shell |
| | | +-------+ | +-------+
| +--------+ | pts/2 |<---------->| shell |
| +-------+ | +-------+
| Kernel |
+-----------------------------+
键盘显示器连接(图形界面)
通过图形界面的Terminal软件 （注意和 键盘显示连接 的区别）
- 使用pseudo terminal (ptmx & pts)
+----------+ +------------+
| Keyboard |------>| |
+----------+ | Terminal |--------------------------+
| Monitor |<------| | fork |
+----------+ +------------+ |
| ↑ |
| | |
write | | read |
| | |
+-----|---|-------------------+ |
| | | | ↓
| ↓ | +-------+ | +-------+
| +--------+ | pts/0 |<---------->| shell |
| | | +-------+ | +-------+
| | ptmx |<->| pts/1 |<---------->| shell |
| | | +-------+ | +-------+
| +--------+ | pts/2 |<---------->| shell |
| +-------+ | +-------+
| Kernel |
+-----------------------------+
pty
pseudo terminal
- PTY slave (shell(bash/zsh…))
- PTY master (terminal emulator (XTerm)) 监听键盘等输入、输出显示内容到XTerm等模拟终端
- tty driver 是master和slave的桥梁
- shell 是一个用户态的程序，可以启动子进程(如：cat)来和内核交互。