pts(7D) 							      Devices								   pts(7D)

NAME

       pts - STREAMS pseudo-tty slave driver

DESCRIPTION

       The  pseudo-tty	subsystem simulates a terminal connection, where the master side represents the terminal and the slave represents the user
       process's special device end point. In order to use the pseudo-tty subsystem, a node for the master side driver /dev/ptmx and N	nodes  for
       the  slave  driver  (N is determined at installation time) must be installed. The names of the slave devices are /dev/pts/M where M has the
       values 0 through N-1. When the master device is opened, the corresponding slave device is automatically locked out. No user may	open  that
       slave  device  until  its  permissions are adjusted and the device unlocked by calling functions grantpt(3C) and unlockpt(3C). The user can
       then invoke the open system call with the name that is returned by the ptsname(3C) function. See the example below.

       Only one open is allowed on a master device. Multiple opens are allowed on the slave device. After both the  master  and  slave	have  been
       opened,	the user has two file descriptors which are end points of a full duplex connection composed of two streams automatically connected
       at the master and slave drivers.  The user may then push modules onto either side of the stream pair. The user needs to push  the  ptem(7M)
       and ldterm(7M) modules onto the slave side of the pseudo-terminal subsystem to get terminal semantics.

       The  master  and slave drivers pass all messages to their adjacent queues.  Only the M_FLUSH needs some processing.  Because the read queue
       of one side is connected to the write queue of the other, the FLUSHR flag is changed to the FLUSHW flag and vice versa.	 When  the  master
       device  is closed an M_HANGUP message is sent to the slave device which will render the device unusable. The process on the slave side gets
       the errno EIO when attempting to write on that stream but it will be able to read any data remaining on the stream head	read  queue.  When
       all  the  data  has  been  read,  read returns 0 indicating that the stream can no longer be used. On the last close of the slave device, a
       0-length message is sent to the master device.  When the application on the master side issues a read() or getmsg() and 0 is returned,  the
       user  of  the  master  device decides whether to issue a close() that dismantles the pseudo-terminal subsystem. If the master device is not
       closed, the pseudo-tty subsystem will be available to another user to open the slave device. Since 0-length messages are used  to  indicate
       that  the  process  on  the slave side has closed and should be interpreted that way by the process on the master side, applications on the
       slave side should not write 0-length messages. If that occurs, the write returns 0, and the 0-length message is discarded by the  ptem mod-
       ule.

       The standard STREAMS system calls can access the pseudo-tty devices.  The slave devices support the O_NDELAY and O_NONBLOCK flags.

EXAMPLES

       int    fdm fds;
       char   *slavename;
       extern char *ptsname();

       fdm = open("/dev/ptmx", O_RDWR);  /* open master */
       grantpt(fdm);			 /* change permission of   slave */
       unlockpt(fdm);			 /* unlock slave */
       slavename = ptsname(fdm);	 /* get name of slave */
       fds = open(slavename, O_RDWR);	 /* open slave */
       ioctl(fds, I_PUSH, "ptem");	 /* push ptem */
       ioctl(fds, I_PUSH, "ldterm");	 /* push ldterm*/

FILES

       /dev/ptmx       master clone device

       /dev/pts/M      slave devices (M = 0 -> N-1)

SEE ALSO

       grantpt(3C), ptsname(3C), unlockpt(3C), ldterm(7M), ptm(7D), ptem(7M)

       STREAMS Programming Guide

SunOS 5.10							    21 Aug 1992 							   pts(7D)