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NAME

     pts - pseudo-terminal driver

DESCRIPTION

     The pts driver provides support for a device-pair termed a
     pseudo-terminal.  A pseudo-terminal is a pair of character devices, a
     master device and a slave device.  The slave device provides to a process
     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.

     The following ioctl(2) calls apply only to pseudo-terminals:

     TIOCPKT       Enable/disable packet mode.  Packet mode is enabled by
                   specifying (by reference) a nonzero parameter and disabled
                   by specifying (by reference) a zero parameter.  When
                   applied to the master side of a pseudo-terminal, each
                   subsequent read(2) from the terminal 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 information.  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 VSTOP is ‘^S’ and VSTART 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
                   information to be read from the master side may be detected
                   by a select(2) for exceptional conditions.

                   This mode is used by rlogin(1) and rlogind(8) 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.

     TIOCGPTN      Obtain device unit number, which can be used to generate
                   the filename of the pseudo-terminal slave device. This
                   ioctl(2) should not be used directly. Instead, the
                   ptsname(3) function should be used.

     TIOCPTMASTER  Determine whether the file descriptor is pointing to a
                   pseudo-terminal master device.  This ioctl(2) should not be
                   used directly. It is used to implement routines like
                   grantpt(3).

     The maximum number of pseudo-terminals is limited to 1000.  It is not
     possible to use more than 1000 pseudo-terminals, as all software which
     use utmp(5) will not be able to handle pseudo-terminals with number
     superior to 999.

FILES

     The files used by this pseudo-terminals implementation are:

     /dev/ptmx       Control device, returns a file descriptor to a new master
                     pseudo-terminal when opened.  This device should not be
                     opened directly.  It’s only available for binary
                     compatibility.  New devices should only be allocated with
                     posix_openpt(2) and openpty(3).

     /dev/pts/[num]  Pseudo-terminal slave devices.

SYSCTL VARIABLES

     The following sysctl(8) variables can be used to modify or monitor pts
     behavior.

     kern.pts_maxdev
             Highest pseudo-terminal unit number to be allocated.  Because
             utmp(5) is restricted to an 8-byte line name size, pts will not
             create any pseudo-terminals with a unit number above 999 by
             default.  After increasing UT_LINESIZE, this variable can be
             changed to allow more than 1000 pseudo-terminals to be allocated
             simultaneously.

DIAGNOSTICS

     None.

SEE ALSO

     grantpt(3), posix_openpt(2), ptsname(3), pty(4), tty(4)

HISTORY

     A pseudo-terminal driver appeared in 4.2BSD.  In FreeBSD 8.0, it was
     replaced with the pts driver.