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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).

       ┌─────────────────────────────────────┬───────────────┬────────────────┐
       │InterfaceAttributeValue          │
       ├─────────────────────────────────────┼───────────────┼────────────────┤
       │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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