man3/ttyslot.3

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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 2017-09-15 "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 .PP
  34 .B "int ttyslot(void);"
  35 .PP
  36 .in -4n
  37 Feature Test Macro Requirements for glibc (see
  38 .BR feature_test_macros (7)):
  39 .in
  40 .PP
  41 .ad l
  42 .BR ttyslot ():
  43 .RS 4
  44 Since glibc 2.24:
  45     _DEFAULT_SOURCE
  46 .br
  47 From glibc 2.20 to 2.23:
  48     _DEFAULT_SOURCE ||
  49     _XOPEN_SOURCE\ &&\ _XOPEN_SOURCE\ <\ 500
  50 .br
  51 Glibc 2.19 and earlier:
  52     _BSD_SOURCE ||
  53     _XOPEN_SOURCE\ &&\ _XOPEN_SOURCE\ <\ 500
  54 .RE
  55 .ad b
  56 .SH DESCRIPTION
  57 The legacy function
  58 .BR ttyslot ()
  59 returns the index of the current user's entry in some file.
  60 .PP
  61 Now "What file?" you ask.
  62 Well, let's first look at some history.
  63 .SS Ancient history
  64 There used to be a file
  65 .I /etc/ttys
  66 in UNIX\ V6, that was read by the
  67 .BR init (1)
  68 program to find out what to do with each terminal line.
  69 Each line consisted of three characters.
  70 The first character was either \(aq0\(aq or \(aq1\(aq,
  71 where \(aq0\(aq meant "ignore".
  72 The second character denoted the terminal: \(aq8\(aq stood for "/dev/tty8".
  73 The third character was an argument to
  74 .BR getty (8)
  75 indicating the sequence of line speeds to try (\(aq\-\(aq was: start trying
  76 110 baud).
  77 Thus a typical line was "18\-".
  78 A hang on some line was solved by changing the \(aq1\(aq to a \(aq0\(aq,
  79 signaling init, changing back again, and signaling init again.
  80 .PP
  81 In UNIX\ V7 the format was changed: here the second character
  82 was the argument to
  83 .BR getty (8)
  84 indicating the sequence of line speeds to try (\(aq0\(aq was: cycle through
  85 300-1200-150-110 baud; \(aq4\(aq was for the on-line console DECwriter)
  86 while the rest of the line contained the name of the tty.
  87 Thus a typical line was "14console".
  88 .PP
  89 Later systems have more elaborate syntax.
  90 System V-like systems have
  91 .I /etc/inittab
  92 instead.
  93 .SS Ancient history (2)
  94 On the other hand, there is the file
  95 .I /etc/utmp
  96 listing the people currently logged in.
  97 It is maintained by
  98 .BR login (1).
  99 It has a fixed size, and the appropriate index in the file was
 100 determined by
 101 .BR login (1)
 102 using the
 103 .BR ttyslot ()
 104 call to find the number of the line in
 105 .I /etc/ttys
 106 (counting from 1).
 107 .SS The semantics of ttyslot
 108 Thus, the function
 109 .BR ttyslot ()
 110 returns the index of the controlling terminal of the calling process
 111 in the file
 112 .IR /etc/ttys ,
 113 and that is (usually) the same as the index of the entry for the
 114 current user in the file
 115 .IR /etc/utmp .
 116 BSD still has the
 117 .I /etc/ttys
 118 file, but System V-like systems do not, and hence cannot refer to it.
 119 Thus, on such systems the documentation says that
 120 .BR ttyslot ()
 121 returns the current user's index in the user accounting data base.
 122 .SH RETURN VALUE
 123 If successful, this function returns the slot number.
 124 On error (e.g., if none of the file descriptors 0, 1 or 2 is
 125 associated with a terminal that occurs in this data base)
 126 it returns 0 on UNIX\ V6 and V7 and BSD-like systems,
 127 but \-1 on System V-like systems.
 128 .SH ATTRIBUTES
 129 For an explanation of the terms used in this section, see
 130 .BR attributes (7).
 131 .TS
 132 allbox;
 133 lb lb lb
 134 l l l.
 135 Interface       Attribute       Value
 136 T{
 137 .BR ttyslot ()
 138 T}      Thread safety   MT-Unsafe
 139 .TE
 140 .SH CONFORMING TO
 141 SUSv1; marked as LEGACY in SUSv2; removed in POSIX.1-2001.
 142 SUSv2 requires \-1 on error.
 143 .SH NOTES
 144 The utmp file is found in various places on various systems, such as
 145 .IR /etc/utmp ,
 146 .IR /var/adm/utmp ,
 147 .IR /var/run/utmp .
 148 .PP
 149 The glibc2 implementation of this function reads the file
 150 .BR _PATH_TTYS ,
 151 defined in
 152 .I <ttyent.h>
 153 as "/etc/ttys".
 154 It returns 0 on error.
 155 Since Linux systems do not usually have "/etc/ttys", it will
 156 always return 0.
 157 .PP
 158 On BSD-like systems and Linux, the declaration of
 159 .BR ttyslot ()
 160 is provided by
 161 .IR <unistd.h> .
 162 On System V-like systems, the declaration is provided by
 163 .IR <stdlib.h> .
 164 Since glibc 2.24,
 165 .IR <stdlib.h>
 166 also provides the declaration with the following
 167 feature test macro definitions:
 168 .PP
 169 .in +4n
 170 .EX
 171 (_XOPEN_SOURCE >= 500 ||
 172         (_XOPEN_SOURCE && _XOPEN_SOURCE_EXTENDED))
 173     && ! (_POSIX_C_SOURCE >= 200112L || _XOPEN_SOURCE >= 600)
 174 .EE
 175 .in
 176 .PP
 177 Minix also has
 178 .IR fttyslot ( fd ).
 179 .\" .SH HISTORY
 180 .\" .BR ttyslot ()
 181 .\" appeared in UNIX V7.
 182 .SH SEE ALSO
 183 .BR getttyent (3),
 184 .BR ttyname (3),
 185 .BR utmp (5)