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 2010-09-20 "GNU" "Linux Programmer's Manual"
28 ttyslot \- find the slot of the current user's terminal in some file
30 .BR "#include <unistd.h>" " /* on BSD-like systems, and Linux */"
32 .BR "#include <stdlib.h>" " /* on System V-like systems */"
34 .B "int ttyslot(void);"
37 Feature Test Macro Requirements for glibc (see
38 .BR feature_test_macros (7)):
46 _XOPEN_SOURCE\ &&\ _XOPEN_SOURCE_\ <\ 500\ &&\ _XOPEN_SOURCE_EXTENDED
52 returns the index of the current user's entry in some file.
54 Now "What file?" you ask.
55 Well, let's first look at some history.
57 There used to be a file
59 in UNIX V6, that was read by the
61 program to find out what to do with each terminal line.
62 Each line consisted of three characters.
63 The first character was either \(aq0\(aq or \(aq1\(aq,
64 where \(aq0\(aq meant "ignore".
65 The second character denoted the terminal: \(aq8\(aq stood for "/dev/tty8".
66 The third character was an argument to
68 indicating the sequence of line speeds to try (\(aq\-\(aq was: start trying
70 Thus a typical line was "18\-".
71 A hang on some line was solved by changing the \(aq1\(aq to a \(aq0\(aq,
72 signaling init, changing back again, and signaling init again.
74 In UNIX V7 the format was changed: here the second character
77 indicating the sequence of line speeds to try (\(aq0\(aq was: cycle through
78 300-1200-150-110 baud; \(aq4\(aq was for the on-line console DECwriter)
79 while the rest of the line contained the name of the tty.
80 Thus a typical line was "14console".
82 Later systems have more elaborate syntax.
83 System V-like systems have
86 .SS "Ancient History (2)"
87 On the other hand, there is the file
89 listing the people currently logged in.
92 It has a fixed size, and the appropriate index in the file was
97 call to find the number of the line in
100 .SS "The semantics of ttyslot"
103 returns the index of the controlling terminal of the calling process
106 and that is (usually) the same as the index of the entry for the
107 current user in the file
111 file, but System V-like systems do not, and hence cannot refer to it.
112 Thus, on such systems the documentation says that
114 returns the current user's index in the user accounting data base.
116 If successful, this function returns the slot number.
117 On error (e.g., if none of the file descriptors 0, 1 or 2 is
118 associated with a terminal that occurs in this data base)
119 it returns 0 on UNIX V6 and V7 and BSD-like systems,
120 but \-1 on System V-like systems.
122 SUSv1; marked as LEGACY in SUSv2; removed in POSIX.1-2001.
123 SUSv2 requires \-1 on error.
125 The utmp file is found various places on various systems, such as
130 The glibc2 implementation of this function reads the file
135 It returns 0 on error.
136 Since Linux systems do not usually have "/etc/ttys", it will
143 .\" appeared in UNIX V7.