Name
ttyslot — find the slot of the current user's terminal in some file
Synopsis
#include <unistd.h> /* See NOTES */
int
ttyslot( |
void); |
![[Note]](../stylesheet/note.png) |
Note | |||||
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DESCRIPTION
The legacy function ttyslot() returns the index of the current
user's entry in some file.
Now "What file?" you ask. Well, let's first look at some history.
Ancient history
There used to be a file /etc/ttys in UNIX V6, that was read by
the init(1) program to find out
what to do with each terminal line. Each line consisted of
three characters. The first character was either '0' or
'1', where '0' meant "ignore". The second character denoted
the terminal: '8' stood for "/dev/tty8". The third
character was an argument to getty(8) indicating the
sequence of line speeds to try ('−' was: start trying
110 baud). Thus a typical line was "18−". A hang on
some line was solved by changing the '1' to a '0',
signaling init, changing back again, and signaling init
again.
In UNIX V7 the format was changed: here the second character was the argument to getty(8) indicating the sequence of line speeds to try ('0' was: cycle through 300-1200-150-110 baud; '4' was for the on-line console DECwriter) while the rest of the line contained the name of the tty. Thus a typical line was "14console".
Later systems have more elaborate syntax. System V-like
systems have /etc/inittab
instead.
Ancient history (2)
On the other hand, there is the file /etc/utmp listing the people currently
logged in. It is maintained by login(1). It has a fixed
size, and the appropriate index in the file was determined
by login(1) using the
ttyslot() call to find the
number of the line in /etc/ttys (counting from 1).
The semantics of ttyslot
Thus, the function ttyslot() returns the index of the
controlling terminal of the calling process in the file
/etc/ttys, and that is
(usually) the same as the index of the entry for the
current user in the file /etc/utmp. BSD still has the /etc/ttys file, but System V-like systems
do not, and hence cannot refer to it. Thus, on such systems
the documentation says that ttyslot() returns the current user's
index in the user accounting data base.
RETURN VALUE
If successful, this function returns the slot number. On error (e.g., if none of the file descriptors 0, 1, or 2 is associated with a terminal that occurs in this data base) it returns 0 on UNIX V6 and V7 and BSD-like systems, but −1 on System V-like systems.
ATTRIBUTES
For an explanation of the terms used in this section, see attributes(7).
| Interface | Attribute | Value |
ttyslot() |
Thread safety | MT-Unsafe |
CONFORMING TO
SUSv1; marked as LEGACY in SUSv2; removed in POSIX.1-2001. SUSv2 requires −1 on error.
NOTES
The utmp file is found in various places on various
systems, such as /etc/utmp,
/var/adm/utmp, /var/run/utmp.
The glibc2 implementation of this function reads the file
_PATH_TTYS, defined in
<ttyent.h>
as "/etc/ttys". It returns 0 on error. Since Linux systems do
not usually have "/etc/ttys", it will always return 0.
On BSD-like systems and Linux, the declaration of
ttyslot() is provided by
<unistd.h>
On System V-like systems, the declaration is provided by
<stdlib.h>
Since glibc 2.24, <stdlib.h>
also provides the declaration with the following feature test
macro definitions:
(_XOPEN_SOURCE >= 500 || (_XOPEN_SOURCE && _XOPEN_SOURCE_EXTENDED)) && ! (_POSIX_C_SOURCE >= 200112L || _XOPEN_SOURCE >= 600)
Minix also has fttyslot(fd).
COLOPHON
This page is part of release 5.13 of the Linux man-pages project. A
description of the project, information about reporting bugs,
and the latest version of this page, can be found at
https://www.kernel.org/doc/man−pages/.
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Copyright (C) 2002 Andries Brouwer <aebcwi.nl> %%%LICENSE_START(VERBATIM) Permission is granted to make and distribute verbatim copies of this manual provided the copyright notice and this permission notice are preserved on all copies. Permission is granted to copy and distribute modified versions of this manual under the conditions for verbatim copying, provided that the entire resulting derived work is distributed under the terms of a permission notice identical to this one. Since the Linux kernel and libraries are constantly changing, this manual page may be incorrect or out-of-date. The author(s) assume no responsibility for errors or omissions, or for damages resulting from the use of the information contained herein. The author(s) may not have taken the same level of care in the production of this manual, which is licensed free of charge, as they might when working professionally. Formatted or processed versions of this manual, if unaccompanied by the source, must acknowledge the copyright and authors of this work. %%%LICENSE_END This replaces an earlier man page written by Walter Harms <walter.harmsinformatik.uni-oldenburg.de>. |