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.\" $FreeBSD: src/lib/libc/sys/posix_openpt.2,v 1.1 2008/08/20 08:31:58 ed Exp $
.\"
.Dd September 10, 2009
.Dt POSIX_OPENPT 3
.Os
.Sh NAME
.Nm posix_openpt
.Nd "open a pseudo-terminal device"
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.In stdlib.h
.In fcntl.h
.Ft int
.Fn posix_openpt "int oflag"
.Sh DESCRIPTION
The
.Fn posix_openpt
function allocates a new pseudo-terminal and establishes a connection
with its master device.
A slave device shall be created in
.Pa /dev/pts .
After the pseudo-terminal has been allocated, the slave will already
have the proper permissions (see
.Xr grantpt 3 )
without the need to call
.Xr grantpt 3 .
The name of the slave device can be determined by calling
.Xr ptsname 3 .
.Pp
The file status flags and file access modes of the open file description
shall be set according to the value of
.Fa oflag .
Values for
.Fa oflag
are constructed by a bitwise-inclusive OR of flags from the following
list, defined in
.In fcntl.h :
.Bl -tag -width ".Dv O_NOCTTY"
.It Dv O_RDWR
Open for reading and writing.
.It Dv O_NOCTTY
If set
.Fn posix_openpt
shall not cause the terminal device to become the controlling terminal
for the process.
.El
.Pp
The
.Fn posix_openpt
function shall fail when
.Fa oflag
contains other values.
.Sh RETURN VALUES
Upon successful completion, the
.Fn posix_openpt
function shall allocate a new pseudo-terminal device and return a
non-negative integer representing a file descriptor, which is connected
to its master device.
Otherwise, -1 shall be returned and errno set to indicate the error.
.Sh ERRORS
The
.Fn posix_openpt
function shall fail if:
.Bl -tag -width Er
.It Bq Er ENFILE
The system file table is full.
.It Bq Er EINVAL
The value of
.Fa oflag
is not valid.
.El
.Sh SEE ALSO
.Xr open 2 ,
.Xr grantpt 3 ,
.Xr ptsname 3 ,
.Xr unlockpt 3 ,
.Xr tty 4
.Sh RATIONALE
The standards committee did not want to directly expose the cloning device and
thus decided to wrap the functionality in this function.
The equivalent code would be:
.Bd -literal
	int
	posix_openpt(int oflag) {
		return open("/dev/ptmx", oflag);
	}
.Ed
.Sh STANDARDS
The
.Fn posix_openpt
function conforms to
.St -p1003.1-2001 .
.Sh HISTORY
The
.Fn posix_openpt
function appeared in
.Dx 2.3 .
.Sh NOTES
The
.Fn posix_openpt
is equivalent in
.Dx
to calling
.Xr open 2
on
.Pa /dev/ptmx .
.Pp
The flag
.Dv O_NOCTTY
is included for compatibility; in
.Dx ,
opening a terminal does not cause it to become a process's controlling
terminal.