PTY(7M)PTY(7M)NAME
pty, pts - pseudo terminal driver
DESCRIPTION
The pty driver provides 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 processes an interface identical to
that described in termio(7). However, whereas all other devices which
provide the interface described in termio(7) 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 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 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 t_stopc is ^S and t_startc is ^Q.
TIOCPKT_NOSTOP
whenever the start and stop characters are not ^S/^Q.
This mode is used by rlogin(1C) and rlogind(1M) 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.
Page 1
PTY(7M)PTY(7M)ALLOCATION
The code sequence shown below demonstrates how to allocate pseudo
terminals. Pseudo terminals, like all files, must have the correct file
permissions to be accessible. The _getpty(3) library function takes care
of this problem.
#include <fcntl.h>
#include <unistd.h>
/*
* Find a pseudo tty to use and open both sides.
* filedes[0] receives the master file descriptor while filedes[1]
* receives the slave. The master is opened with O_NDELAY as commonly
* needed in daemons such as rlogind and telnetd.
*/
int /* -1 on failure */
findPseudoTTY(int *filedes)
{
char *line;
line = _getpty(&filedes[0], O_RDWR|O_NDELAY, 0600, 0);
if (0 == line)
return -1;
if (0 > (filedes[1] = open(line, O_RDWR))) {
(void)close(filedes[0]);
return -1;
}
return 0;
}
CONFIGURATION
The maximum number of pseudo ttys allowed on a system is controlled by
the maxpty variable setting in /var/sysgen/master.d/ptc. The default is
1000, but this may be increased to 2000. Values larger than 2000 are not
supported.
FILES
/dev/ptc - master pseudo terminal
/dev/tty[qrstuvwxyz][0-199] - slave pseudo terminals
/dev/pts - equivalent to /dev/ttyq[0-9]
/var/sysgen/master.d/ptc - device configuration
SEE ALSOgetpty(3)
Page 2
