trusty (3) posix_openpt.3posix.gz
NAME
posix_openpt - open a pseudo-terminal device
SYNOPSIS
#include <stdlib.h> #include <fcntl.h> int posix_openpt(int oflag);
DESCRIPTION
The posix_openpt() function shall establish a connection between a master device for a pseudo-terminal
and a file descriptor. The file descriptor is used by other I/O functions that refer to that pseudo-
terminal.
The file status flags and file access modes of the open file description shall be set according to the
value of oflag.
Values for oflag are constructed by a bitwise-inclusive OR of flags from the following list, defined in
<fcntl.h>:
O_RDWR Open for reading and writing.
O_NOCTTY
If set posix_openpt() shall not cause the terminal device to become the controlling terminal for
the process.
The behavior of other values for the oflag argument is unspecified.
RETURN VALUE
Upon successful completion, the posix_openpt() function shall open a master pseudo-terminal device and
return a non-negative integer representing the lowest numbered unused file descriptor. Otherwise, -1
shall be returned and errno set to indicate the error.
ERRORS
The posix_openpt() function shall fail if:
EMFILE {OPEN_MAX} file descriptors are currently open in the calling process.
ENFILE The maximum allowable number of files is currently open in the system.
The posix_openpt() function may fail if:
EINVAL The value of oflag is not valid.
EAGAIN Out of pseudo-terminal resources.
ENOSR Out of STREAMS resources.
The following sections are informative.
EXAMPLES
Opening a Pseudo-Terminal and Returning the Name of the Slave
Device and a File Descriptor
#include <fcntl.h>
#include <stdio.h>
int masterfd, slavefd;
char *slavedevice;
masterfd = posix_openpt(O_RDWR|O_NOCTTY);
if (masterfd == -1
|| grantpt (masterfd) == -1
|| unlockpt (masterfd) == -1
|| (slavedevice = ptsname (masterfd)) == NULL)
return -1;
printf("slave device is: %s\n", slavedevice);
slavefd = open(slave, O_RDWR|O_NOCTTY);
if (slavefd < 0)
return -1;
APPLICATION USAGE
This function is a method for portably obtaining a file descriptor of a master terminal device for a
pseudo-terminal. The grantpt() and ptsname() functions can be used to manipulate mode and ownership
permissions, and to obtain the name of the slave device, respectively.
RATIONALE
The standard developers considered the matter of adding a special device for cloning master pseudo-
terminals: the /dev/ptmx device. However, consensus could not be reached, and it was felt that adding a
new function would permit other implementations. The posix_openpt() function is designed to complement
the grantpt(), ptsname(), and unlockpt() functions.
On implementations supporting the /dev/ptmx clone device, opening the master device of a pseudo-terminal
is simply:
mfdp = open("/dev/ptmx", oflag );
if (mfdp < 0)
return -1;
FUTURE DIRECTIONS
None.
SEE ALSO
grantpt() , open() , ptsname() , unlockpt() , the Base Definitions volume of IEEE Std 1003.1-2001,
<fcntl.h>
COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2003 Edition,
Standard for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of Electrical and Electronics Engineers,
Inc and The Open Group. In the event of any discrepancy between this version and the original IEEE and
The Open Group Standard, the original IEEE and The Open Group Standard is the referee document. The
original Standard can be obtained online at http://www.opengroup.org/unix/online.html .