From kde-core-devel  Sat Apr 15 15:32:16 2006
From: Thiago Macieira <thiago () kde ! org>
Date: Sat, 15 Apr 2006 15:32:16 +0000
To: kde-core-devel
Subject: Re: KProcess overhaul
Message-Id: <200604151732.17479.thiago () kde ! org>
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Ralf Habacker wrote:
>> 9. on unix, it should be able to deal with ptys
>> =A0
>
>Can you explain a non unix user for what this is good ?

A PTY (Pseudo-Teletype) is a special device that terminal programs use in=20
Unix. Each process has one Controlling TTY, which is the terminal they=20
are associated with.

Originally, the TTYs were serial ports, when computers were accessed using=
=20
dumb terminals. On Linux, today, the Virtual Terminals are TTYs. Also, we=20
have the pseudo ones that, instead of being connected to a device (serial=20
port, printer, monitor+keyboard, dumb terminal, etc.), are like pipes: a=20
program behind the scenes receives the output and sends the input.

The easiest way to understand this is the telnet daemon: when a new=20
connection is received, it opens a new pty and runs the user's shell in=20
there. When the user types (i.e., when the telnet server receives data on=20
its network socket), it sends data over the pty to the shell. When the=20
shell outputs something, the server receives data on the pty and sends it=20
back over the network socket. The shell and terminal programs cannot tell=20
apart a pty from a real terminal.

Think of pty as special pipes. The difference here is that the API to open=
=20
a new PTY (open the master, discover the name of the slave, etc.), set it=20
up, fork the child process and set the PTY as its controlling terminal=20
varies quite a bit between OSes.

=2D-=20
Thiago Macieira  -  thiago (AT) macieira.info - thiago (AT) kde.org
  thiago.macieira (AT) trolltech.com     Trolltech AS
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