thiago at kde.org
Sat Apr 15 16:32:16 BST 2006
Ralf Habacker wrote:
>> 9. on unix, it should be able to deal with ptys
>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
Unix. Each process has one Controlling TTY, which is the terminal they
are associated with.
Originally, the TTYs were serial ports, when computers were accessed using
dumb terminals. On Linux, today, the Virtual Terminals are TTYs. Also, we
have the pseudo ones that, instead of being connected to a device (serial
port, printer, monitor+keyboard, dumb terminal, etc.), are like pipes: a
program behind the scenes receives the output and sends the input.
The easiest way to understand this is the telnet daemon: when a new
connection is received, it opens a new pty and runs the user's shell in
there. When the user types (i.e., when the telnet server receives data on
its network socket), it sends data over the pty to the shell. When the
shell outputs something, the server receives data on the pty and sends it
back over the network socket. The shell and terminal programs cannot tell
apart a pty from a real terminal.
Think of pty as special pipes. The difference here is that the API to open
a new PTY (open the master, discover the name of the slave, etc.), set it
up, fork the child process and set the PTY as its controlling terminal
varies quite a bit between OSes.
Thiago Macieira - thiago (AT) macieira.info - thiago (AT) kde.org
thiago.macieira (AT) trolltech.com Trolltech AS
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