grantpt(3) — Linux manual page


GRANTPT(3)              Linux Programmer's Manual             GRANTPT(3)

NAME         top

       grantpt - grant access to the slave pseudoterminal

SYNOPSIS         top

       #include <stdlib.h>

       int grantpt(int fd);

   Feature Test Macro Requirements for glibc (see

           Since glibc 2.24:
               _XOPEN_SOURCE >= 500
           Glibc 2.23 and earlier:

DESCRIPTION         top

       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         top

       When successful, grantpt() returns 0.  Otherwise, it returns -1
       and sets errno to indicate the error.

ERRORS         top

       EACCES The corresponding slave pseudoterminal could not be

       EBADF  The fd argument is not a valid open file descriptor.

       EINVAL The fd argument is valid but not associated with a master

VERSIONS         top

       grantpt() is provided in glibc since version 2.1.

ATTRIBUTES         top

       For an explanation of the terms used in this section, see

       │Interface                      Attribute     Value          │
       │grantpt()                      │ Thread safety │ MT-Safe locale │

CONFORMING TO         top

       POSIX.1-2001, POSIX.1-2008.

NOTES         top

       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 absent during the
       glibc build that is typical on many systems).

SEE ALSO         top

       open(2), posix_openpt(3), ptsname(3), unlockpt(3), pts(4), pty(7)

COLOPHON         top

       This page is part of release 5.13 of the Linux man-pages project.
       A description of the project, information about reporting bugs,
       and the latest version of this page, can be found at

GNU                            2021-03-22                     GRANTPT(3)

Pages that refer to this page: getpt(3)posix_openpt(3)ptsname(3)unlockpt(3)pts(4)pty(7)