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
pseudoterminal device corresponding to the master pseudoterminal re-
ferred 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 un-
specified 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
pseudoterminal.
ATTRIBUTES
For an explanation of the terms used in this section, see attrib-
utes(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 pseudotermi-
nals; this support has been removed. On modern systems this is either
a no-op —with permissions configured on pty allocation, as is the case
on Linux— or an ioctl(2).
SEE ALSO
open(2), posix_openpt(3), ptsname(3), unlockpt(3), pts(4), pty(7)
Linux man-pages 6.7 2023-10-31 grantpt(3)
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