man3/ttyslot.3

   1 .\" Copyright (C) 2002 Andries Brouwer <aeb@cwi.nl>
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  23 .\" This replaces an earlier man page written by Walter Harms
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  26 .TH TTYSLOT 3 2002-07-20 "GNU" "Linux Programmer's Manual"
  27 .SH NAME
  28 ttyslot \- find the slot of the current user's terminal in some file
  29 .SH SYNOPSIS
  30 .sp
  31 .BR "#include <unistd.h>"       "    /* on BSD-like systems  */"
  32 .br
  33 .BR "#include <stdlib.h>"       "    /* on System V-like systems */"
  34 .sp
  35 .B "int ttyslot(void);"
  36 .SH DESCRIPTION
  37 The legacy function
  38 .BR ttyslot ()
  39 returns the index of the current user's entry in some file.
  40 .LP
  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 (8)
  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 '0' or '1', where '0' meant "ignore".
  51 The second character denoted the terminal: '8' stood for "/dev/tty8".
  52 The third character was an argument to
  53 .BR getty (8)
  54 indicating the sequence of line speeds to try ('\-' was: start trying
  55 110 baud).
  56 Thus a typical line was "18\-".
  57 A hang on some line was solved by changing the '1' to a '0',
  58 signalling init, changing back again, and signalling init again.
  59 .LP
  60 In Unix V7 the format was changed: here the second character
  61 was the argument to
  62 .BR getty (8)
  63 indicating the sequence of line speeds to try ('0' was: cycle through
  64 300-1200-150-110 baud; '4' was for the on-line console DECwriter)
  65 while the rest of the line contained the name of the tty.
  66 Thus a typical line was "14console".
  67 .LP
  68 Later systems have more elaborate syntax.
  69 System V-like systems have
  70 .I /etc/inittab
  71 instead.
  72 .SS "Ancient History (2)"
  73 On the other hand, there is the file
  74 .I /etc/utmp
  75 listing the people currently logged in.
  76 It is maintained by
  77 .BR login (8).
  78 It has a fixed size, and the appropriate index in the file was
  79 determined by
  80 .BR login (8)
  81 using the
  82 .BR ttyslot ()
  83 call to find the number of the line in
  84 .IR /etc/ttys
  85 (counting from 1).
  86 .SS "The semantics of ttyslot"
  87 Thus, the function
  88 .BR ttyslot ()
  89 returns the index of the controlling terminal of the current process
  90 in the file
  91 .IR /etc/ttys ,
  92 and that is (usually) the same as the index of the entry for the
  93 current user in the file
  94 .IR /etc/utmp .
  95 BSD still has the
  96 .I /etc/ttys
  97 file, but System V-like systems do not, and hence cannot refer to it.
  98 Thus, on such systems the documentation says that
  99 .BR ttyslot ()
 100 returns the current user's index in the user accounting data base.
 101 .SH "RETURN VALUE"
 102 If successful, this function returns the slot number.
 103 On error (e.g., if none of the file descriptors 0, 1 or 2 is
 104 associated with a terminal that occurs in this data base)
 105 it returns 0 on Unix V6 and V7 and BSD-like systems,
 106 but \-1 on System V-like systems.
 107 .SH NOTES
 108 The utmp file is found various places on various systems, such as
 109 .IR /etc/utmp ,
 110 .IR /var/adm/utmp ,
 111 .IR /var/run/utmp .
 112 .LP
 113 The glibc2 implementation of this function reads the file
 114 .BR _PATH_TTYS ,
 115 defined in
 116 .I <ttyent.h>
 117 as "/etc/ttys".
 118 It returns 0 on error.
 119 Since Linux systems do not usually have "/etc/ttys", it will
 120 always return 0.
 121 .LP
 122 Minix also has
 123 .IR fttyslot ( fd ).
 124 .\" .SH HISTORY
 125 .\" .BR ttyslot ()
 126 .\" appeared in Unix V7.
 127 .SH "CONFORMING TO"
 128 SUSv1; marked as LECACY in SUSv2; removed in POSIX.1-2001.
 129 SUSv2 requires \-1 on error.
 130 .SH "SEE ALSO"
 131 .BR getttyent (3),
 132 .BR ttyname (3),
 133 .BR utmp (5)