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>.
28 .TH TTYSLOT 3 2013-07-22 "GNU" "Linux Programmer's Manual"
30 ttyslot \- find the slot of the current user's terminal in some file
32 .BR "#include <unistd.h>" " /* on BSD-like systems, and Linux */"
34 .BR "#include <stdlib.h>" " /* on System V-like systems */"
36 .B "int ttyslot(void);"
39 Feature Test Macro Requirements for glibc (see
40 .BR feature_test_macros (7)):
48 _XOPEN_SOURCE\ &&\ _XOPEN_SOURCE_\ <\ 500\ &&\ _XOPEN_SOURCE_EXTENDED
54 returns the index of the current user's entry in some file.
56 Now "What file?" you ask.
57 Well, let's first look at some history.
59 There used to be a file
61 in UNIX\ V6, that was read by the
63 program to find out what to do with each terminal line.
64 Each line consisted of three characters.
65 The first character was either \(aq0\(aq or \(aq1\(aq,
66 where \(aq0\(aq meant "ignore".
67 The second character denoted the terminal: \(aq8\(aq stood for "/dev/tty8".
68 The third character was an argument to
70 indicating the sequence of line speeds to try (\(aq\-\(aq was: start trying
72 Thus a typical line was "18\-".
73 A hang on some line was solved by changing the \(aq1\(aq to a \(aq0\(aq,
74 signaling init, changing back again, and signaling init again.
76 In UNIX\ V7 the format was changed: here the second character
79 indicating the sequence of line speeds to try (\(aq0\(aq was: cycle through
80 300-1200-150-110 baud; \(aq4\(aq was for the on-line console DECwriter)
81 while the rest of the line contained the name of the tty.
82 Thus a typical line was "14console".
84 Later systems have more elaborate syntax.
85 System V-like systems have
88 .SS Ancient history (2)
89 On the other hand, there is the file
91 listing the people currently logged in.
94 It has a fixed size, and the appropriate index in the file was
99 call to find the number of the line in
102 .SS The semantics of ttyslot
105 returns the index of the controlling terminal of the calling process
108 and that is (usually) the same as the index of the entry for the
109 current user in the file
113 file, but System V-like systems do not, and hence cannot refer to it.
114 Thus, on such systems the documentation says that
116 returns the current user's index in the user accounting data base.
118 If successful, this function returns the slot number.
119 On error (e.g., if none of the file descriptors 0, 1 or 2 is
120 associated with a terminal that occurs in this data base)
121 it returns 0 on UNIX\ V6 and V7 and BSD-like systems,
122 but \-1 on System V-like systems.
124 .SS Multithreading (see pthreads(7))
127 function calls thread-unsafe function
129 so it is not thread-safe.
131 SUSv1; marked as LEGACY in SUSv2; removed in POSIX.1-2001.
132 SUSv2 requires \-1 on error.
134 The utmp file is found various places on various systems, such as
139 The glibc2 implementation of this function reads the file
144 It returns 0 on error.
145 Since Linux systems do not usually have "/etc/ttys", it will
152 .\" appeared in UNIX V7.
158 This page is part of release 3.79 of the Linux
161 A description of the project,
162 information about reporting bugs,
163 and the latest version of this page,
165 \%http://www.kernel.org/doc/man\-pages/.