freebsd-dev/lib/libc/stdlib/grantpt.3

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.Dd December 23, 2002
.Os
.Dt GRANTPT 3
.Sh NAME
.Nm grantpt ,
.Nm ptsname ,
.Nm unlockpt ,
.Nm posix_openpt
.Nd pseudo-terminal access functions
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.In stdlib.h
.Ft int
.Fn grantpt "int fildes"
.Ft "char *"
.Fn ptsname "int fildes"
.Ft int
.Fn unlockpt "int fildes"
.In fcntl.h
.Ft int
.Fn posix_openpt "int mode"
.Sh DESCRIPTION
The
.Fn grantpt ,
.Fn ptsname ,
.Fn unlockpt ,
and
.Fn posix_openpt
functions allow access to pseudo-terminal devices.
The first three functions accept a file descriptor
that references the master half of a pseudo-terminal pair.
This file descriptor is created with
.Fn posix_openpt .
.Pp
The
.Fn grantpt
function is used to establish ownership and permissions
of the slave device counterpart to the master device
specified with
.Fa fildes .
The slave device's ownership is set to the real user ID
of the calling process, and the permissions are set to
user readable-writable and group writable.
The group owner of the slave device is also set to the
group
.Dq Li tty
if it exists on the system; otherwise, it
is left untouched.
.Pp
The
.Fn ptsname
function returns the full pathname of the slave device
counterpart to the master device specified with
.Fa fildes .
This value can be used
to subsequently open the appropriate slave after
.Fn posix_openpt
and
.Fn grantpt
have been called.
.Pp
The
.Fn unlockpt
function clears the lock held on the pseudo-terminal pair
for the master device specified with
.Fa fildes .
.Pp
The
.Fn posix_openpt
function opens the first available master pseudo-terminal
device and returns a descriptor to it.
The
.Fa mode
argument
specifies the flags used for opening the device:
.Bl -tag -width ".Dv O_NOCTTY"
.It Dv O_RDWR
Open for reading and writing.
.It Dv O_NOCTTY
If set, do not allow the terminal to become
the controlling terminal for the calling process.
.El
.Sh RETURN VALUES
.Rv -std grantpt unlockpt
.Pp
The
.Fn ptsname
function returns a pointer to the name
of the slave device on success; otherwise a
.Dv NULL
pointer is returned and the global variable
.Va errno
is set to indicate the error.
.Pp
The
.Fn posix_openpt
function returns a file descriptor to the first
available master pseudo-terminal device on success;
otherwise \-1 is returned and the global variable
.Va errno
is set to indicate the error.
.Sh ERRORS
The
.Fn grantpt ,
.Fn ptsname ,
and
.Fn unlockpt
functions may fail and set
.Va errno
to:
.Bl -tag -width Er
.It Bq Er EINVAL
.Fa fildes
is not a master pseudo-terminal device.
.El
.Pp
In addition, the
.Fn grantpt
function may set
.Va errno
to:
.Bl -tag -width Er
.It Bq Er EACCES
The slave pseudo-terminal device could not be accessed.
.El
.Pp
The
.Fn posix_openpt
function may fail and set
.Va errno
to:
.Bl -tag -width Er
.It Bq Er EINVAL
.Fa mode
consists of an invalid mode bit.
.It Bq Er EAGAIN
The system has no available pseudo-terminal devices.
.El
.Pp
The
.Fn grantpt ,
.Fn ptsname ,
and
.Fn unlockpt
functions may also fail and set
.Va errno
for any of the errors specified for the
.Xr fstat 2
system call.
.Pp
The
.Fn posix_openpt
function may also fail and set
.Va errno
for any of the errors specified for the
.Xr open 2
system call.
.Sh SEE ALSO
.Xr open 2 ,
.Xr pty 4 ,
.Xr tty 4
.Sh STANDARDS
The
.Fn grantpt ,
.Fn ptsname ,
.Fn unlockpt ,
and
.Fn posix_openpt
functions conform to
.St -p1003.1-2001 .
.Sh HISTORY
The
.Fn grantpt ,
.Fn ptsname ,
.Fn unlockpt ,
and
.Fn posix_openpt
functions appeared in
.Fx 5.0 .
.Sh NOTES
The purpose of the
.Fn unlockpt
function has no meaning in
.Fx .
.Pp
The flag
.Dv O_NOCTTY
is included for compatibility; in
.Fx ,
opening a terminal does not cause it to become
a process's controlling terminal.