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Thu Nov 2 09:08:48 EST 2006

In AIX Version 4, the pty subsystem uses naming conventions similar
to those from UNIX System V. There is one node for the control driver,
/dev/ptc, and a maximum number of N nodes for the slave drivers, /dev/pts/n.
N is configurable at pty configuration and may be changed dynamically
by pty reconfiguration, without closing the opened devices.

The control device is set up as a clone device whose major device
number is the clone device's major number and whose minor device number
is the control driver's major number. There is no node in the filesystem
for control devices. A control device can be opened only once, but
slave devices can be opened several times.

By opening the control device with the /dev/ptc special file, an application
can quickly open the control and slave sides of an unused pseudo-terminal.
The name of the corresponding slave side can be retrieved using the
ttyname subroutine, which always returns the name of the slave side.

Implementation Specifics

This file is part of Base Operating System (BOS) Runtime.

With Berkeley pty subsystems, commands have to search for an unused
pseudo-terminal by opening each control side sequentially. The control
side could not be opened if it was already in use. Thus, the opens
would fail, setting the errno variable to EIO, until an unused pseudo-terminal
was found. It is possible to configure the pty subsystem in order
to use special files with the BSD pty naming convention:

Control devices /dev/pty[p-zA-Z][0-f]

Slave devices   /dev/tty[p-zA-Z][0-f]

These special files are not symbolic links to the AIX special files.
The BSD special files are completely separate from the AIX special
files. The number of control and slave pair devices using the BSD
naming convention is configurable.

In version 3 of the operating system, the pty subsystem used two multiplexed
special files, /dev/ptc and /dev/pts. These special files no longer
exist, but the procedure for opening a pty device is the same.

$ ls -l /dev/ptc
crw-rw-rw-   1 root     system    11, 24 Apr 30 1999  /dev/ptc
$ tty
$ ls -l /dev/pts/1
crw--w--w-   1 alleni   teacher   25,  1 Feb 19 04:27 /dev/pts/1
$ ls -l /dev/pts/99
crw-rw-rw-   1 root     system    25, 99 Apr 25 2001  /dev/pts/99

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