PTSNAME(3) BSD Library Functions Manual PTSNAME(3)NAME
grantpt, ptsname, unlockpt — pseudo-terminal access functions
Standard C Library (libc, -lc)
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(2).
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
The ptsname() function returns the full pathname 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(2)
and grantpt() have been called.
The unlockpt() function clears the lock held on the pseudo-terminal pair
for the master device specified with fildes.
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.
The grantpt() 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
SEE ALSOposix_openpt(2), pts(4), tty(4)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(2) 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.
The grantpt(), ptsname() and unlockpt() functions appeared in
BSD August 20, 2008 BSD