NAME
grantpt, ptsname,
unlockpt —
pseudo-terminal access
functions
SYNOPSIS
#include
<stdlib.h>
int
grantpt(int
fildes);
char *
ptsname(int
fildes);
int
unlockpt(int
fildes);
DESCRIPTION
The
grantpt(),
ptsname(), and unlockpt()
functions allow access to pseudo-terminal devices. These three functions
accept a file descriptor that references the master half of a
pseudo-terminal pair. This file descriptor is created with
posix_openpt(3).
The
grantpt()
function is used to establish ownership and permissions of the slave device
counterpart to the master device specified with
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 “tty”.
The
ptsname()
function returns the full path name of the slave device counterpart to the
master device specified with fildes. This value can be
used to subsequently open the appropriate slave after
posix_openpt(3) and grantpt() have been
called.
The
unlockpt()
function clears the lock held on the pseudo-terminal pair for the master
device specified with fildes.
RETURN VALUES
The grantpt() and
unlockpt() functions return the value 0 if
successful; otherwise the value -1 is returned and the global
variable errno is set to indicate the error.
The ptsname() function returns a pointer
to the name of the slave device on success; otherwise a
NULL pointer is returned.
ERRORS
The grantpt(),
ptsname() and unlockpt()
functions may fail and set errno to:
- [
EBADF] - fildes is not a valid open file descriptor.
- [
EINVAL] - fildes is not a master pseudo-terminal device.
In addition, the grantpt() function may
set errno to:
- [
EACCES] - The slave pseudo-terminal device could not be accessed.
SEE ALSO
STANDARDS
The ptsname() function conforms to
IEEE Std 1003.1-2008 (“POSIX.1”).
This implementation of grantpt() and
unlockpt() does not conform to IEEE
Std 1003.1-2008 (“POSIX.1”), because it depends on
posix_openpt(3) to create the pseudo-terminal device with proper
permissions in place. It only validates whether fildes
is a valid pseudo-terminal master device. Future revisions of the
specification will likely allow this behaviour, as stated by the Austin
Group.
HISTORY
The grantpt(),
ptsname() and unlockpt()
functions appeared in OpenBSD 5.3.