man3/grantpt.3

   1 .\" %%%LICENSE_START(PUBLIC_DOMAIN)
   2 .\" This page is in the public domain. - aeb
   3 .\" %%%LICENSE_END
   4 .\"
   5 .TH GRANTPT 3 2017-09-15 "GNU" "Linux Programmer's Manual"
   6 .SH NAME
   7 grantpt \- grant access to the slave pseudoterminal
   8 .SH SYNOPSIS
   9 .B #include <stdlib.h>
  10 .PP
  11 .BI "int grantpt(int " fd ");"
  12 .PP
  13 .in -4n
  14 Feature Test Macro Requirements for glibc (see
  15 .BR feature_test_macros (7)):
  16 .in
  17 .PP
  18 .ad l
  19 .BR grantpt ():
  20 .br
  21 .RS 4
  22 Since glibc 2.24:
  23     _XOPEN_SOURCE\ >=\ 500 ||
  24         (_XOPEN_SOURCE\ &&\ _XOPEN_SOURCE_EXTENDED)
  25 .br
  26 Glibc 2.23 and earlier:
  27     _XOPEN_SOURCE
  28 .RE
  29 .ad
  30 .SH DESCRIPTION
  31 The
  32 .BR grantpt ()
  33 function changes the mode and owner of the slave pseudoterminal device
  34 corresponding to the master pseudoterminal referred to by
  35 .IR fd .
  36 The user ID of the slave is set to the real UID of the calling process.
  37 The group ID is set to an unspecified value (e.g.,
  38 .IR tty ).
  39 The mode of the slave is set to 0620 (crw\-\-w\-\-\-\-).
  40 .PP
  41 The behavior of
  42 .BR grantpt ()
  43 is unspecified if a signal handler is installed to catch
  44 .B SIGCHLD
  45 signals.
  46 .SH RETURN VALUE
  47 When successful,
  48 .BR grantpt ()
  49 returns 0.
  50 Otherwise, it returns \-1 and sets
  51 .I errno
  52 appropriately.
  53 .SH ERRORS
  54 .TP
  55 .B EACCES
  56 The corresponding slave pseudoterminal could not be accessed.
  57 .TP
  58 .B EBADF
  59 The
  60 .I fd
  61 argument is not a valid open file descriptor.
  62 .TP
  63 .B EINVAL
  64 The
  65 .I fd
  66 argument is valid but not associated with a master pseudoterminal.
  67 .SH VERSIONS
  68 .BR grantpt ()
  69 is provided in glibc since version 2.1.
  70 .SH ATTRIBUTES
  71 For an explanation of the terms used in this section, see
  72 .BR attributes (7).
  73 .TS
  74 allbox;
  75 lb lb lb
  76 l l l.
  77 Interface       Attribute       Value
  78 T{
  79 .BR grantpt ()
  80 T}      Thread safety   MT-Safe locale
  81 .TE
  82 .sp 1
  83 .SH CONFORMING TO
  84 POSIX.1-2001, POSIX.1-2008.
  85 .SH NOTES
  86 This is part of the UNIX 98 pseudoterminal support, see
  87 .BR pts (4).
  88 .PP
  89 Many systems implement this function via a set-user-ID helper binary
  90 called "pt_chown".
  91 On Linux systems with a devpts filesystem (present since Linux 2.2),
  92 the kernel normally sets the correct ownership and permissions
  93 for the pseudoterminal slave when the master is opened
  94 .RB ( posix_openpt (3)),
  95 so that nothing must be done by
  96 .BR grantpt ().
  97 Thus, no such helper binary is required
  98 (and indeed it is configured to be absent during the
  99 glibc build that is typical on many systems).
 100 .SH SEE ALSO
 101 .BR open (2),
 102 .BR posix_openpt (3),
 103 .BR ptsname (3),
 104 .BR unlockpt (3),
 105 .BR pts (4),
 106 .BR pty (7)