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 module.
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 5.11 21 Aug 1992 pts(7D)