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'\" t
.\" %%%LICENSE_START(PUBLIC_DOMAIN)
.\" This page is in the public domain. - aeb
.\" %%%LICENSE_END
.\"
.TH grantpt 3 2024-05-02 "Linux man-pages 6.8"
.SH NAME
grantpt \- grant access to the slave pseudoterminal
.SH LIBRARY
Standard C library
.RI ( libc ", " \-lc )
.SH SYNOPSIS
.nf
.B #include <stdlib.h>
.P
.BI "int grantpt(int " fd ");"
.fi
.P
.RS -4
Feature Test Macro Requirements for glibc (see
.BR feature_test_macros (7)):
.RE
.P
.BR grantpt ():
.nf
Since glibc 2.24:
_XOPEN_SOURCE >= 500
.\" || (_XOPEN_SOURCE && _XOPEN_SOURCE_EXTENDED)
glibc 2.23 and earlier:
_XOPEN_SOURCE
.fi
.SH DESCRIPTION
The
.BR grantpt ()
function changes the mode and owner of the slave pseudoterminal device
corresponding to the master pseudoterminal referred to by the file descriptor
.IR 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.,
.IR tty ).
The mode of the slave is set to 0620 (crw\-\-w\-\-\-\-).
.P
The behavior of
.BR grantpt ()
is unspecified if a signal handler is installed to catch
.B SIGCHLD
signals.
.SH RETURN VALUE
When successful,
.BR grantpt ()
returns 0.
Otherwise, it returns \-1 and sets
.I errno
to indicate the error.
.SH ERRORS
.TP
.B EACCES
The corresponding slave pseudoterminal could not be accessed.
.TP
.B EBADF
The
.I fd
argument is not a valid open file descriptor.
.TP
.B EINVAL
The
.I fd
argument is valid but not associated with a master pseudoterminal.
.SH ATTRIBUTES
For an explanation of the terms used in this section, see
.BR attributes (7).
.TS
allbox;
lbx lb lb
l l l.
Interface Attribute Value
T{
.na
.nh
.BR grantpt ()
T} Thread safety MT-Safe locale
.TE
.SH STANDARDS
POSIX.1-2008.
.SH HISTORY
glibc 2.1.
POSIX.1-2001.
.P
This is part of the UNIX 98 pseudoterminal support, see
.BR pts (4).
.P
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
.BR ioctl (2).
.SH SEE ALSO
.BR open (2),
.BR posix_openpt (3),
.BR ptsname (3),
.BR unlockpt (3),
.BR pts (4),
.BR pty (7)
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