NAME
ttyslot - find the slot of the current user's terminal in some file
SYNOPSIS
R #include <unistd.h> /* on BSD-like systems */
R #include <stdlib.h> /* on System V-like systems */
int ttyslot(void);
DESCRIPTION
The legacy function
R 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(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
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(8).
It has a fixed size, and the appropriate index in the file was
determined by
login(8)
using the
R ttyslot ()
call to find the number of the line in
R /etc/ttys
(counting from 1).
The semantics of ttyslot
Thus, the function
R ttyslot ()
returns the index of the controlling terminal of the current process
in the file
R /etc/ttys ,
and that is (usually) the same as the index of the entry for the
current user in the file
R /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
R 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.
CONFORMING TO
SUSv1; marked as LECACY in SUSv2; removed in POSIX.1-2001.
SUSv2 requires -1 on error.
NOTES
The utmp file is found various places on various systems, such as
R /etc/utmp ,
R /var/adm/utmp ,
R /var/run/utmp .
The glibc2 implementation of this function reads the file
R _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.
Minix also has
R fttyslot ( fd ).
SEE ALSO
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