#include <stdlib.h> #include <fcntl.h>
The posix_openpt() function establishes 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 are 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() does not cause the terminal device to become the controlling terminal for the process.
The behavior of other values for the oflag argument is unspecified.
Upon successful completion, the posix_openpt() function opens a master pseudo-terminal device and returns a non-negative integer representing the lowest numbered unused file descriptor. Otherwise, -1 is returned and errno is set to indicate the error.
The posix_openpt() function will 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.
Example 1: Open a pseudo-terminal.
The following example opens a pseudo-terminal and returns 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;
This function provieds a method for portably obtaining a file descriptor of a master terminal device for a pseudo-terminal. The grantpt(3C) and ptsname(3C) functions can be used to manipulate mode and ownership permissions and to obtain the name of the slave device, respectively.
See attributes(5) for descriptions of the following attributes:
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
| Interface Stability | Standard |
| MT-Level | MT-Safe |
open(2), grantpt(3C), ptsname(3C), unlockpt(3C), attributes(5), standards(5)