man3/ttyslot.3

   1 '\" t
   2 .\" Copyright (C) 2002 Andries Brouwer <aeb@cwi.nl>
   3 .\"
   4 .\" SPDX-License-Identifier: Linux-man-pages-copyleft
   5 .\"
   6 .\" This replaces an earlier man page written by Walter Harms
   7 .\" <walter.harms@informatik.uni-oldenburg.de>.
   8 .\"
   9 .TH ttyslot 3 (date) "Linux man-pages (unreleased)"
  10 .SH NAME
  11 ttyslot \- find the slot of the current user's terminal in some file
  12 .SH LIBRARY
  13 Standard C library
  14 .RI ( libc ", " \-lc )
  15 .SH SYNOPSIS
  16 .nf
  17 .BR "#include <unistd.h>" "       /* See NOTES */"
  18 .P
  19 .B "int ttyslot(void);"
  20 .fi
  21 .P
  22 .RS -4
  23 Feature Test Macro Requirements for glibc (see
  24 .BR feature_test_macros (7)):
  25 .RE
  26 .P
  27 .BR ttyslot ():
  28 .nf
  29     Since glibc 2.24:
  30         _DEFAULT_SOURCE
  31     From glibc 2.20 to glibc 2.23:
  32         _DEFAULT_SOURCE || (_XOPEN_SOURCE && _XOPEN_SOURCE < 500)
  33     glibc 2.19 and earlier:
  34         _BSD_SOURCE || (_XOPEN_SOURCE && _XOPEN_SOURCE < 500)
  35 .fi
  36 .SH DESCRIPTION
  37 The legacy function
  38 .BR ttyslot ()
  39 returns the index of the current user's entry in some file.
  40 .P
  41 Now "What file?" you ask.
  42 Well, let's first look at some history.
  43 .SS Ancient history
  44 There used to be a file
  45 .I /etc/ttys
  46 in UNIX\ V6, that was read by the
  47 .BR init (1)
  48 program to find out what to do with each terminal line.
  49 Each line consisted of three characters.
  50 The first character was either \[aq]0\[aq] or \[aq]1\[aq],
  51 where \[aq]0\[aq] meant "ignore".
  52 The second character denoted the terminal: \[aq]8\[aq] stood for "/dev/tty8".
  53 The third character was an argument to
  54 .BR getty (8)
  55 indicating the sequence of line speeds to try (\[aq]\-\[aq] was: start trying
  56 110 baud).
  57 Thus a typical line was "18\-".
  58 A hang on some line was solved by changing the \[aq]1\[aq] to a \[aq]0\[aq],
  59 signaling init, changing back again, and signaling init again.
  60 .P
  61 In UNIX\ V7 the format was changed: here the second character
  62 was the argument to
  63 .BR getty (8)
  64 indicating the sequence of line speeds to try (\[aq]0\[aq] was: cycle through
  65 300-1200-150-110 baud; \[aq]4\[aq] was for the on-line console DECwriter)
  66 while the rest of the line contained the name of the tty.
  67 Thus a typical line was "14console".
  68 .P
  69 Later systems have more elaborate syntax.
  70 System V-like systems have
  71 .I /etc/inittab
  72 instead.
  73 .SS Ancient history (2)
  74 On the other hand, there is the file
  75 .I /etc/utmp
  76 listing the people currently logged in.
  77 It is maintained by
  78 .BR login (1).
  79 It has a fixed size, and the appropriate index in the file was
  80 determined by
  81 .BR login (1)
  82 using the
  83 .BR ttyslot ()
  84 call to find the number of the line in
  85 .I /etc/ttys
  86 (counting from 1).
  87 .SS The semantics of ttyslot
  88 Thus, the function
  89 .BR ttyslot ()
  90 returns the index of the controlling terminal of the calling process
  91 in the file
  92 .IR /etc/ttys ,
  93 and that is (usually) the same as the index of the entry for the
  94 current user in the file
  95 .IR /etc/utmp .
  96 BSD still has the
  97 .I /etc/ttys
  98 file, but System V-like systems do not, and hence cannot refer to it.
  99 Thus, on such systems the documentation says that
 100 .BR ttyslot ()
 101 returns the current user's index in the user accounting data base.
 102 .SH RETURN VALUE
 103 If successful, this function returns the slot number.
 104 On error (e.g., if none of the file descriptors 0, 1, or 2 is
 105 associated with a terminal that occurs in this data base)
 106 it returns 0 on UNIX\ V6 and V7 and BSD-like systems,
 107 but \-1 on System V-like systems.
 108 .SH ATTRIBUTES
 109 For an explanation of the terms used in this section, see
 110 .BR attributes (7).
 111 .TS
 112 allbox;
 113 lbx lb lb
 114 l l l.
 115 Interface       Attribute       Value
 116 T{
 117 .na
 118 .nh
 119 .BR ttyslot ()
 120 T}      Thread safety   MT-Unsafe
 121 .TE
 122 .SH VERSIONS
 123 The utmp file is found in various places on various systems, such as
 124 .IR /etc/utmp ,
 125 .IR /var/adm/utmp ,
 126 .IR /var/run/utmp .
 127 .SH STANDARDS
 128 None.
 129 .SH HISTORY
 130 SUSv1; marked as LEGACY in SUSv2; removed in POSIX.1-2001.
 131 SUSv2 requires \-1 on error.
 132 .P
 133 The glibc2 implementation of this function reads the file
 134 .BR _PATH_TTYS ,
 135 defined in
 136 .I <ttyent.h>
 137 as "/etc/ttys".
 138 It returns 0 on error.
 139 Since Linux systems do not usually have "/etc/ttys", it will
 140 always return 0.
 141 .P
 142 On BSD-like systems and Linux, the declaration of
 143 .BR ttyslot ()
 144 is provided by
 145 .IR <unistd.h> .
 146 On System V-like systems, the declaration is provided by
 147 .IR <stdlib.h> .
 148 Since glibc 2.24,
 149 .I <stdlib.h>
 150 also provides the declaration with the following
 151 feature test macro definitions:
 152 .P
 153 .in +4n
 154 .EX
 155 (_XOPEN_SOURCE >= 500 ||
 156         (_XOPEN_SOURCE && _XOPEN_SOURCE_EXTENDED))
 157     && ! (_POSIX_C_SOURCE >= 200112L || _XOPEN_SOURCE >= 600)
 158 .EE
 159 .in
 160 .P
 161 Minix also has
 162 .IR fttyslot ( fd ).
 163 .\" .SH HISTORY
 164 .\" .BR ttyslot ()
 165 .\" appeared in UNIX V7.
 166 .SH SEE ALSO
 167 .BR getttyent (3),
 168 .BR ttyname (3),
 169 .BR utmp (5)