pty

PTY(4)                      Kernel Interfaces Manual                    PTY(4)

NAME
     pty — BSD-style and System V-style compatibility pseudo-terminal driver

SYNOPSIS
     device pty

DESCRIPTION
     The pty driver provides support for the traditional BSD naming scheme
     that was used for accessing pseudo-terminals.  When the device /dev/ptyXX
     is being opened, a new terminal shall be created with the pts(4) driver.
     A device node for this terminal shall be created, which has the name
     /dev/ttyXX.

     The pty driver also provides a cloning System V /dev/ptmx device.

     New code should not try to allocate pseudo-terminals using this
     interface.  It is only provided for compatibility with older C libraries
     that tried to open such devices when posix_openpt(2) was being called.

FILES
     The BSD-style compatibility pseudo-terminal driver uses the following
     device names:

     /dev/pty[l-sL-S][0-9a-v]  Pseudo-terminal master devices.

     /dev/tty[l-sL-S][0-9a-v]  Pseudo-terminal slave devices.

     /dev/ptmx                 Control device, returns a file descriptor to a
                               new master pseudo-terminal when opened.

DIAGNOSTICS
     None.

SEE ALSO
     posix_openpt(2), pts(4), tty(4)

HISTORY
     A pseudo-terminal driver appeared in 4.2BSD.

BUGS
     Unlike previous implementations, the master and slave device nodes are
     destroyed when the PTY becomes unused.  A call to stat(2) on a
     nonexistent master device will already cause a new master device node to
     be created.  The master device can only be destroyed by opening and
     closing it.

     The pty driver cannot be unloaded, because it cannot determine if it is
     being used.

                                August 20, 2008