linux 终端的几个概念

http://askubuntu.com/questions/14284/why-is-a-virtual-terminal-virtual-and-what-why-where-is-the-real-terminal

模拟终端在以前是一种设备， The Teletype workstations would have been called "Consoles" or "Terminals", a virtual terminal, as opposed to a real one, thus is any application or machinery that provides the same functionality as this workplace arrangement - which is accessing the computer by sending keystrokes to it and receiving output back from it, printing it to a piece of paper. You can imagine that a Modem works in a very similar way.

Terminal Emulators, such as the one pictured above, are cheap and simple computers that emulatethe functionality of a teletype. When we say terminal emulator these days, we - in turn - usually mean a program that emulates the functionality of such a machine.

今天说模拟终端的时候，可能是一种程序。

pty是一种模拟的tty， pts 是pty的一种实现。

tty号是： linux的 1--7.  

虚拟终端数明显可以超过7个。

[root@localhost ~]# who
root     pts/0        2015-10-10 13:58 (192.168.2.1)
root     pts/2        2015-10-10 15:11 (192.168.2.1)
root     tty1         2015-10-10 15:04 (:0)
root     pts/1        2015-10-10 15:10 (:0.0)
root     pts/3        2015-10-10 15:11 (192.168.2.1)
root     pts/4        2015-10-10 15:11 (192.168.2.1)
root     pts/5        2015-10-10 15:11 (192.168.2.1)
root     pts/6        2015-10-10 15:11 (192.168.2.1)
root     pts/7        2015-10-10 15:11 (192.168.2.1)
root     pts/8        2015-10-10 15:11 (192.168.2.1)