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grantpt
Section: C Library Functions (3) Updated: 2025-09-21 Index
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NAME
grantpt - grant access to the slave pseudoterminal
LIBRARY
Standard C library
( libc,~ -lc)
SYNOPSIS
#define _XOPEN_SOURCE
#include <stdlib.h>
int grantpt(int fd);
Feature Test Macro Requirements for glibc (see
feature_test_macros(7)):
grantpt():
Since glibc 2.24:
_XOPEN_SOURCE >= 500
glibc 2.23 and earlier:
_XOPEN_SOURCE
DESCRIPTION
The
grantpt()
function changes the mode and owner of the slave pseudoterminal device
corresponding to the master pseudoterminal referred to by the file descriptor
fd.
The user ID of the slave is set to the real UID of the calling process.
The group ID is set to an unspecified value (e.g.,
tty).
The mode of the slave is set to 0620 (crw--w----).
The behavior of
grantpt()
is unspecified if a signal handler is installed to catch
SIGCHLD
signals.
RETURN VALUE
When successful,
grantpt()
returns 0.
Otherwise, it returns -1 and sets
errno
to indicate the error.
ERRORS
- EACCES
-
The corresponding slave pseudoterminal could not be accessed.
- EBADF
-
The
fd
argument is not a valid open file descriptor.
- EINVAL
-
The
fd
argument is valid but not associated with a master pseudoterminal.
ATTRIBUTES
For an explanation of the terms used in this section, see
attributes(7).
| Interface | Attribute | Value
|
|
grantpt()
| Thread safety | MT-Safe locale
|
STANDARDS
POSIX.1-2008.
HISTORY
glibc 2.1.
POSIX.1-2001.
This is part of the UNIX 98 pseudoterminal support, see
pts(4).
Historical systems implemented this function via a set-user-ID helper binary
called "pt_chown".
glibc on Linux before glibc 2.33 could do so as well,
in order to support configurations with only BSD pseudoterminals;
this support has been removed.
On modern systems this is either a no-op
[em]with permissions configured on pty allocation, as is the case on Linux[em]
or an
ioctl(2).
SEE ALSO
open(2),
posix_openpt(3),
ptsname(3),
unlockpt(3),
pts(4),
pty(7)
Index
- NAME
-
- LIBRARY
-
- SYNOPSIS
-
- DESCRIPTION
-
- RETURN VALUE
-
- ERRORS
-
- ATTRIBUTES
-
- STANDARDS
-
- HISTORY
-
- SEE ALSO
-
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