man3/ttyslot.3

   1 .\" Copyright (C) 2002 Andries Brouwer <aeb@cwi.nl>
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  25 .\" This replaces an earlier man page written by Walter Harms
  26 .\" <walter.harms@informatik.uni-oldenburg.de>.
  27 .\"
  28 .TH TTYSLOT 3 2016-03-15 "GNU" "Linux Programmer's Manual"
  29 .SH NAME
  30 ttyslot \- find the slot of the current user's terminal in some file
  31 .SH SYNOPSIS
  32 .BR "#include <unistd.h>" "       /See NOTES */"
  33 .sp
  34 .B "int ttyslot(void);"
  35 .sp
  36 .in -4n
  37 Feature Test Macro Requirements for glibc (see
  38 .BR feature_test_macros (7)):
  39 .in
  40 .sp
  41 .ad l
  42 .BR ttyslot ():
  43 .RS 4
  44 Since glibc 2.20:
  45     _BSD_SOURCE ||
  46     _XOPEN_SOURCE\ &&\ _XOPEN_SOURCE_\ <\ 500
  47 .br
  48 Glibc 2.19 and earlier:
  49     _DEFAULT_SOURCE ||
  50     _XOPEN_SOURCE\ &&\ _XOPEN_SOURCE_\ <\ 500
  51 .RE
  52 .ad b
  53 .SH DESCRIPTION
  54 The legacy function
  55 .BR ttyslot ()
  56 returns the index of the current user's entry in some file.
  57 .LP
  58 Now "What file?" you ask.
  59 Well, let's first look at some history.
  60 .SS Ancient history
  61 There used to be a file
  62 .I /etc/ttys
  63 in UNIX\ V6, that was read by the
  64 .BR init (1)
  65 program to find out what to do with each terminal line.
  66 Each line consisted of three characters.
  67 The first character was either \(aq0\(aq or \(aq1\(aq,
  68 where \(aq0\(aq meant "ignore".
  69 The second character denoted the terminal: \(aq8\(aq stood for "/dev/tty8".
  70 The third character was an argument to
  71 .BR getty (8)
  72 indicating the sequence of line speeds to try (\(aq\-\(aq was: start trying
  73 110 baud).
  74 Thus a typical line was "18\-".
  75 A hang on some line was solved by changing the \(aq1\(aq to a \(aq0\(aq,
  76 signaling init, changing back again, and signaling init again.
  77 .LP
  78 In UNIX\ V7 the format was changed: here the second character
  79 was the argument to
  80 .BR getty (8)
  81 indicating the sequence of line speeds to try (\(aq0\(aq was: cycle through
  82 300-1200-150-110 baud; \(aq4\(aq was for the on-line console DECwriter)
  83 while the rest of the line contained the name of the tty.
  84 Thus a typical line was "14console".
  85 .LP
  86 Later systems have more elaborate syntax.
  87 System V-like systems have
  88 .I /etc/inittab
  89 instead.
  90 .SS Ancient history (2)
  91 On the other hand, there is the file
  92 .I /etc/utmp
  93 listing the people currently logged in.
  94 It is maintained by
  95 .BR login (1).
  96 It has a fixed size, and the appropriate index in the file was
  97 determined by
  98 .BR login (1)
  99 using the
 100 .BR ttyslot ()
 101 call to find the number of the line in
 102 .I /etc/ttys
 103 (counting from 1).
 104 .SS The semantics of ttyslot
 105 Thus, the function
 106 .BR ttyslot ()
 107 returns the index of the controlling terminal of the calling process
 108 in the file
 109 .IR /etc/ttys ,
 110 and that is (usually) the same as the index of the entry for the
 111 current user in the file
 112 .IR /etc/utmp .
 113 BSD still has the
 114 .I /etc/ttys
 115 file, but System V-like systems do not, and hence cannot refer to it.
 116 Thus, on such systems the documentation says that
 117 .BR ttyslot ()
 118 returns the current user's index in the user accounting data base.
 119 .SH RETURN VALUE
 120 If successful, this function returns the slot number.
 121 On error (e.g., if none of the file descriptors 0, 1 or 2 is
 122 associated with a terminal that occurs in this data base)
 123 it returns 0 on UNIX\ V6 and V7 and BSD-like systems,
 124 but \-1 on System V-like systems.
 125 .SH ATTRIBUTES
 126 For an explanation of the terms used in this section, see
 127 .BR attributes (7).
 128 .TS
 129 allbox;
 130 lb lb lb
 131 l l l.
 132 Interface       Attribute       Value
 133 T{
 134 .BR ttyslot ()
 135 T}      Thread safety   MT-Unsafe
 136 .TE
 137 .SH CONFORMING TO
 138 SUSv1; marked as LEGACY in SUSv2; removed in POSIX.1-2001.
 139 SUSv2 requires \-1 on error.
 140 .SH NOTES
 141 The utmp file is found in various places on various systems, such as
 142 .IR /etc/utmp ,
 143 .IR /var/adm/utmp ,
 144 .IR /var/run/utmp .
 145 .LP
 146 The glibc2 implementation of this function reads the file
 147 .BR _PATH_TTYS ,
 148 defined in
 149 .I <ttyent.h>
 150 as "/etc/ttys".
 151 It returns 0 on error.
 152 Since Linux systems do not usually have "/etc/ttys", it will
 153 always return 0.
 154 .PP
 155 On BSD-like systems and Linux, the declaration of
 156 .BR ttyslot ()
 157 is provided by
 158 .IR <unistd.h> .
 159 On Systsem V-like systems, the declaration is provided by
 160 .IR <stdlib.h> .
 161 Since glibc 2.24,
 162 .IR <stdlib.h>
 163 also provides the declaration with the following
 164 feature test macro definitions:
 165 .PP
 166 .nf
 167 .in +4n
 168 (_XOPEN_SOURCE >= 500 ||
 169         (_XOPEN_SOURCE && _XOPEN_SOURCE_EXTENDED))
 170     && ! (_POSIX_C_SOURCE >= 200112L || _XOPEN_SOURCE >= 600)
 171 .in
 172 .fi
 173 .PP
 174 Minix also has
 175 .IR fttyslot ( fd ).
 176 .\" .SH HISTORY
 177 .\" .BR ttyslot ()
 178 .\" appeared in UNIX V7.
 179 .SH SEE ALSO
 180 .BR getttyent (3),
 181 .BR ttyname (3),
 182 .BR utmp (5)