4.3BSD - /usr/man/cat4/pty.0

PTY(4)                                                                  PTY(4)


NAME
       pty - pseudo terminal driver

SYNOPSIS
       pseudo-device pty [ count ]

DESCRIPTION
       The  pty driver provides support for a device-pair termed a pseudo ter���
       minal.  A pseudo terminal is a pair  of  character  devices,  a  master
       device  and  a  slave  device.   The slave device provides processes an
       interface identical to that described in tty(4).  However, whereas  all
       other  devices  which  provide the interface described in tty(4) have a
       hardware device of  some  sort  behind  them,  the  slave  device  has,
       instead, another process manipulating it through the master half of the
       pseudo terminal.  That is, anything written on  the  master  device  is
       given  to  the  slave device as input and anything written on the slave
       device is presented as input on the master device.

       In configuring, if an optional ‘‘count’’ is given in the specification,
       that  number of pseudo terminal pairs are configured; the default count
       is 32.

       The following ioctl calls apply only to pseudo terminals:

       TIOCSTOP
              Stops output to a terminal (e.g.  like  typing  ^S).   Takes  no
              parameter.

       TIOCSTART
              Restarts output (stopped by TIOCSTOP or by typing ^S).  Takes no
              parameter.

       TIOCPKT
              Enable/disable packet mode.  Packet mode is enabled by  specify‐
              ing  (by reference) a nonzero parameter and disabled by specify‐
              ing (by reference) a zero parameter.  When applied to the master
              side  of a pseudo terminal, each subsequent read from the termi‐
              nal will return data written on the slave  part  of  the  pseudo
              terminal  preceded  by  a  zero  byte  (symbolically  defined as
              TIOCPKT_DATA), or a single byte reflecting control status infor‐
              mation.  In the latter case, the byte is an inclusive-or of zero
              or more of the bits:

              TIOCPKT_FLUSHREAD
                     whenever the read queue for the terminal is flushed.

              TIOCPKT_FLUSHWRITE
                     whenever the write queue for the terminal is flushed.

              TIOCPKT_STOP
                     whenever output to the terminal is stopped a la ^S.

              TIOCPKT_START
                     whenever output to the terminal is restarted.

              TIOCPKT_DOSTOP
                     whenever t_stopc is ^S and t_startc is ^Q.

              TIOCPKT_NOSTOP
                     whenever the start and stop characters are not ^S/^Q.

              While this mode is in use, the presence of control status infor‐
              mation  to  be  read  from  the master side may be detected by a
              select for exceptional conditions.

              This mode is used by rlogin(1C) and rlogind(8C) to  implement  a
              remote-echoed,  locally  ^S/^Q flow-controlled remote login with
              proper back-flushing of output; it can be used by other  similar
              programs.

       TIOCUCNTL
              Enable/disable  a mode that allows a small number of simple user
              ioctl commands to be passed through the pseudo-terminal, using a
              protocol  similar to that of TIOCPKT.  The TIOCUCNTL and TIOCPKT
              modes are mutually exclusive.  This mode  is  enabled  from  the
              master  side of a pseudo terminal by specifying (by reference) a
              nonzero parameter and disabled by specifying  (by  reference)  a
              zero  parameter.  Each subsequent read from the master side will
              return data written on the slave part  of  the  pseudo  terminal
              preceded by a zero byte, or a single byte reflecting a user con‐
              trol operation on the slave side.  A user control  command  con‐
              sists  of a special ioctl operation with no data; the command is
              given as UIOCCMD(n), where n is a number  in  the  range  1-255.
              The  operation  value n will be received as a single byte on the
              next read from the master side.  The ioctl UIOCCMD(0) is a no-op
              that  may  be  used to probe for the existence of this facility.
              As with TIOCPKT mode, command operations may be detected with  a
              select for exceptional conditions.

       TIOCREMOTE
              A  mode for the master half of a pseudo terminal, independent of
              TIOCPKT.  This mode causes input to the pseudo  terminal  to  be
              flow controlled and not input edited (regardless of the terminal
              mode).  Each write to the control  terminal  produces  a  record
              boundary for the process reading the terminal.  In normal usage,
              a write of data is like the data typed as a line on  the  termi‐
              nal; a write of 0 bytes is like typing an end-of-file character.
              TIOCREMOTE can be used when doing remote line editing in a  win‐
              dow manager, or whenever flow controlled input is required.

FILES
       /dev/pty[p-r][0-9a-f]    master pseudo terminals
       /dev/tty[p-r][0-9a-f]    slave pseudo terminals

DIAGNOSTICS
       None.


4.2 Berkeley Distribution        May 19, 1986                           PTY(4)