mirror of https://github.com/mkerrisk/man-pages
144 lines
4.7 KiB
Groff
144 lines
4.7 KiB
Groff
.\" Copyright (C) 2002 Andries Brouwer <aeb@cwi.nl>
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.\"
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.\" Permission is granted to make and distribute verbatim copies of this
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.\" manual provided the copyright notice and this permission notice are
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.\" preserved on all copies.
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.\"
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.\" Permission is granted to copy and distribute modified versions of this
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.\" manual under the conditions for verbatim copying, provided that the
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.\" entire resulting derived work is distributed under the terms of a
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.\" permission notice identical to this one.
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.\"
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.\" Since the Linux kernel and libraries are constantly changing, this
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.\" manual page may be incorrect or out-of-date. The author(s) assume no
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.\" responsibility for errors or omissions, or for damages resulting from
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.\" the use of the information contained herein. The author(s) may not
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.\" have taken the same level of care in the production of this manual,
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.\" which is licensed free of charge, as they might when working
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.\" professionally.
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.\"
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.\" Formatted or processed versions of this manual, if unaccompanied by
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.\" the source, must acknowledge the copyright and authors of this work.
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.\"
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.\" This replaces an earlier man page written by Walter Harms
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.\" <walter.harms@informatik.uni-oldenburg.de>.
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.\"
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.TH TTYSLOT 3 2007-11-26 "GNU" "Linux Programmer's Manual"
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.SH NAME
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ttyslot \- find the slot of the current user's terminal in some file
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.SH SYNOPSIS
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.BR "#include <unistd.h>" " /* on BSD-like systems, and Linux */"
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.br
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.BR "#include <stdlib.h>" " /* on System V-like systems */"
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.sp
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.B "int ttyslot(void);"
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.sp
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.in -4n
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Feature Test Macro Requirements for glibc (see
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.BR feature_test_macros (7)):
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.in
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.sp
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.ad l
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.BR ttyslot ():
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_BSD_SOURCE || (_XOPEN_SOURCE_EXTENDED && !\ _XOPEN_SOURCE\ >=\ 500)
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.ad b
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.SH DESCRIPTION
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The legacy function
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.BR ttyslot ()
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returns the index of the current user's entry in some file.
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.LP
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Now "What file?" you ask.
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Well, let's first look at some history.
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.SS "Ancient History"
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There used to be a file
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.I /etc/ttys
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in Unix V6, that was read by the
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.BR init (8)
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program to find out what to do with each terminal line.
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Each line consisted of three characters.
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The first character was either \(aq0\(aq or \(aq1\(aq,
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where \(aq0\(aq meant "ignore".
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The second character denoted the terminal: \(aq8\(aq stood for "/dev/tty8".
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The third character was an argument to
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.BR getty (8)
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indicating the sequence of line speeds to try (\(aq\-\(aq was: start trying
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110 baud).
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Thus a typical line was "18\-".
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A hang on some line was solved by changing the \(aq1\(aq to a \(aq0\(aq,
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signaling init, changing back again, and signaling init again.
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.LP
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In Unix V7 the format was changed: here the second character
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was the argument to
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.BR getty (8)
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indicating the sequence of line speeds to try (\(aq0\(aq was: cycle through
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300-1200-150-110 baud; \(aq4\(aq was for the on-line console DECwriter)
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while the rest of the line contained the name of the tty.
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Thus a typical line was "14console".
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.LP
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Later systems have more elaborate syntax.
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System V-like systems have
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.I /etc/inittab
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instead.
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.SS "Ancient History (2)"
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On the other hand, there is the file
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.I /etc/utmp
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listing the people currently logged in.
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It is maintained by
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.BR login (1).
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It has a fixed size, and the appropriate index in the file was
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determined by
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.BR login (1)
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using the
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.BR ttyslot ()
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call to find the number of the line in
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.I /etc/ttys
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(counting from 1).
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.SS "The semantics of ttyslot"
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Thus, the function
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.BR ttyslot ()
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returns the index of the controlling terminal of the calling process
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in the file
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.IR /etc/ttys ,
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and that is (usually) the same as the index of the entry for the
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current user in the file
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.IR /etc/utmp .
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BSD still has the
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.I /etc/ttys
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file, but System V-like systems do not, and hence cannot refer to it.
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Thus, on such systems the documentation says that
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.BR ttyslot ()
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returns the current user's index in the user accounting data base.
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.SH "RETURN VALUE"
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If successful, this function returns the slot number.
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On error (e.g., if none of the file descriptors 0, 1 or 2 is
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associated with a terminal that occurs in this data base)
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it returns 0 on Unix V6 and V7 and BSD-like systems,
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but \-1 on System V-like systems.
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.SH "CONFORMING TO"
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SUSv1; marked as LEGACY in SUSv2; removed in POSIX.1-2001.
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SUSv2 requires \-1 on error.
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.SH NOTES
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The utmp file is found various places on various systems, such as
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.IR /etc/utmp ,
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.IR /var/adm/utmp ,
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.IR /var/run/utmp .
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.LP
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The glibc2 implementation of this function reads the file
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.BR _PATH_TTYS ,
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defined in
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.I <ttyent.h>
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as "/etc/ttys".
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It returns 0 on error.
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Since Linux systems do not usually have "/etc/ttys", it will
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always return 0.
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.LP
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Minix also has
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.IR fttyslot ( fd ).
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.\" .SH HISTORY
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.\" .BR ttyslot ()
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.\" appeared in Unix V7.
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.SH "SEE ALSO"
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.BR getttyent (3),
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.BR ttyname (3),
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.BR utmp (5)
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