[thirdparty/man-pages.git] / man3 / ttyslot.3

.\" Copyright (C) 2002 Andries Brouwer <aeb@cwi.nl>
.\"
.\" 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.\" manual page may be incorrect or out-of-date.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.
.\"
.\" This replaces an earlier man page written by Walter Harms
.\" <walter.harms@informatik.uni-oldenburg.de>.
.\"
.TH TTYSLOT 3 2002-07-20 "GNU" "Linux Programmer's Manual"
.SH NAME
ttyslot \- find the slot of the current user's terminal in some file
.SH SYNOPSIS
.sp
.BR "#include <unistd.h>"       "    /* on BSD-like systems  */"
.br
.BR "#include <stdlib.h>"       "    /* on SYSV-like systems */"
.sp
.B "int ttyslot(void);"
.SH DESCRIPTION
The legacy function
.BR ttyslot ()
returns the index of the current user's entry in some file.
.LP
Now "What file?" you ask. Well, let's first look at some history.
.SS "Ancient History"
There used to be a file
.I /etc/ttys
in Unix V6, that was read by the
.BR init (8)
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
.BR 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',
signalling init, changing back again, and signalling init again.
.LP
In Unix V7 the format was changed: here the second character
was the argument to
.BR 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".
.LP
Later systems have more elaborate syntax.
SYSV-like systems have
.I /etc/inittab
instead.
.SS "Ancient History (2)"
On the other hand, there is the file
.I /etc/utmp
listing the people currently logged in. It is maintained by
.BR login (8).
It has a fixed size, and the appropriate index in the file was
determined by
.BR login (8)
using the
.BR ttyslot ()
call to find the number of the line in
.IR /etc/ttys
(counting from 1).
.SS "The semantics of ttyslot"
Thus, the function
.BR ttyslot ()
returns the index of the controlling terminal of the current process
in the file
.IR /etc/ttys ,
and that is (usually) the same as the index of the entry for the
current user in the file
.IR /etc/utmp .
BSD still has the
.I /etc/ttys
file, but SYSV-like systems do not, and hence cannot refer to it.
Thus, on such systems the documentation says that
.BR ttyslot ()
returns the current user's index in the user accounting data base.
.SH "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 SYSV-like systems.
.SH NOTES
The utmp file is found various places on various systems, such as
.IR /etc/utmp ,
.IR /var/adm/utmp ,
.IR /var/run/utmp .
.LP
The glibc2 implementation of this function reads the file
.BR _PATH_TTYS ,
defined in
.I <ttyent.h>
as "/etc/ttys". It returns 0 on error.
Since Linux systems do not usually have "/etc/ttys", it will
always return 0.
.LP
Minix also has
.IR fttyslot ( fd ).
.SH HISTORY
.BR ttyslot ()
appeared in Unix V7.
.SH "CONFORMS TO"
XPG2. Legacy in SUSv2. Deleted in SUSv3.
SUSv2 requires \-1 on error.
.SH "SEE ALSO"
.BR getttyent (3),
.BR ttyname (3),
.BR utmp (5)
Commit	Line	Data
fea681da MK	1	.\" Copyright (C) 2002 Andries Brouwer <aeb@cwi.nl>
	2	.\"
	3	.\" Permission is granted to make and distribute verbatim copies of this
	4	.\" manual provided the copyright notice and this permission notice are
	5	.\" preserved on all copies.
	6	.\"
	7	.\" Permission is granted to copy and distribute modified versions of this
	8	.\" manual under the conditions for verbatim copying, provided that the
	9	.\" entire resulting derived work is distributed under the terms of a
	10	.\" permission notice identical to this one.
	11	.\"
	12	.\" Since the Linux kernel and libraries are constantly changing, this
	13	.\" manual page may be incorrect or out-of-date. The author(s) assume no
	14	.\" responsibility for errors or omissions, or for damages resulting from
	15	.\" the use of the information contained herein. The author(s) may not
	16	.\" have taken the same level of care in the production of this manual,
	17	.\" which is licensed free of charge, as they might when working
	18	.\" professionally.
	19	.\"
	20	.\" Formatted or processed versions of this manual, if unaccompanied by
	21	.\" the source, must acknowledge the copyright and authors of this work.
	22	.\"
	23	.\" This replaces an earlier man page written by Walter Harms
	24	.\" <walter.harms@informatik.uni-oldenburg.de>.
	25	.\"
	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 SYSV-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. Well, let's first look at some history.
	42	.SS "Ancient History"
	43	There used to be a file
	44	.I /etc/ttys
	45	in Unix V6, that was read by the
	46	.BR init (8)
	47	program to find out what to do with each terminal line.
	48	Each line consisted of three characters.
	49	The first character was either '0' or '1', where '0' meant "ignore".
	50	The second character denoted the terminal: '8' stood for "/dev/tty8".
	51	The third character was an argument to
	52	.BR getty (8)
8c383102 MK	53	indicating the sequence of line speeds to try ('\-' was: start trying
8c383102 MK	54	110 baud). Thus a typical line was "18\-".
fea681da MK	55	A hang on some line was solved by changing the '1' to a '0',
	56	signalling init, changing back again, and signalling init again.
	57	.LP
	58	In Unix V7 the format was changed: here the second character
	59	was the argument to
	60	.BR getty (8)
	61	indicating the sequence of line speeds to try ('0' was: cycle through
	62	300-1200-150-110 baud; '4' was for the on-line console DECwriter)
	63	while the rest of the line contained the name of the tty.
	64	Thus a typical line was "14console".
	65	.LP
	66	Later systems have more elaborate syntax.
	67	SYSV-like systems have
	68	.I /etc/inittab
	69	instead.
	70	.SS "Ancient History (2)"
	71	On the other hand, there is the file
	72	.I /etc/utmp
	73	listing the people currently logged in. It is maintained by
	74	.BR login (8).
	75	It has a fixed size, and the appropriate index in the file was
	76	determined by
	77	.BR login (8)
	78	using the
	79	.BR ttyslot ()
	80	call to find the number of the line in
	81	.IR /etc/ttys
	82	(counting from 1).
	83	.SS "The semantics of ttyslot"
	84	Thus, the function
	85	.BR ttyslot ()
	86	returns the index of the controlling terminal of the current process
	87	in the file
	88	.IR /etc/ttys ,
	89	and that is (usually) the same as the index of the entry for the
	90	current user in the file
	91	.IR /etc/utmp .
	92	BSD still has the
	93	.I /etc/ttys
	94	file, but SYSV-like systems do not, and hence cannot refer to it.
	95	Thus, on such systems the documentation says that
	96	.BR ttyslot ()
	97	returns the current user's index in the user accounting data base.
	98	.SH "RETURN VALUE"
	99	If successful, this function returns the slot number.
	100	On error (e.g., if none of the file descriptors 0, 1 or 2 is
	101	associated with a terminal that occurs in this data base)
	102	it returns 0 on Unix V6 and V7 and BSD-like systems,
	103	but \-1 on SYSV-like systems.
	104	.SH NOTES
	105	The utmp file is found various places on various systems, such as
	106	.IR /etc/utmp ,
	107	.IR /var/adm/utmp ,
	108	.IR /var/run/utmp .
	109	.LP
	110	The glibc2 implementation of this function reads the file
	111	.BR _PATH_TTYS ,
	112	defined in
	113	.I <ttyent.h>
	114	as "/etc/ttys". It returns 0 on error.
	115	Since Linux systems do not usually have "/etc/ttys", it will
	116	always return 0.
	117	.LP
	118	Minix also has
119	.IR fttyslot ( fd ).
120	.SH HISTORY
121	.BR ttyslot ()
122	appeared in Unix V7.
123	.SH "CONFORMS TO"
124	XPG2. Legacy in SUSv2. Deleted in SUSv3.
125	SUSv2 requires \-1 on error.
126	.SH "SEE ALSO"
127	.BR getttyent (3),
128	.BR ttyname (3),
129	.BR utmp (5)