grantpt(3) Library Functions Manual grantpt(3)
NAME
grantpt - grant access to the slave pseudoterminal
LIBRARY
Standard C library (libc, -lc)
SYNOPSIS
#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 pseu-
doterminal 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 in-
stalled 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 pseu-
doterminal.
VERSIONS
grantpt() is provided since glibc 2.1.
ATTRIBUTES
For an explanation of the terms used in this section, see at-
tributes(7).
┌─────────────────────────────────────┬───────────────┬────────────────┐
│Interface │ Attribute │ Value │
├─────────────────────────────────────┼───────────────┼────────────────┤
│grantpt() │ Thread safety │ MT-Safe locale │
└─────────────────────────────────────┴───────────────┴────────────────┘
STANDARDS
POSIX.1-2001, POSIX.1-2008.
NOTES
This is part of the UNIX 98 pseudoterminal support, see pts(4).
Many systems implement this function via a set-user-ID helper binary
called "pt_chown". On Linux systems with a devpts filesystem (present
since Linux 2.2), the kernel normally sets the correct ownership and
permissions for the pseudoterminal slave when the master is opened
(posix_openpt(3)), so that nothing must be done by grantpt(). Thus, no
such helper binary is required (and indeed it is configured to be ab-
sent during the glibc build that is typical on many systems).
SEE ALSO
open(2), posix_openpt(3), ptsname(3), unlockpt(3), pts(4), pty(7)
Linux man-pages 6.03 2023-02-05 grantpt(3)
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