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(8)
program to find out what to do with each terminal line.
Each line consisted of three characters.
The first character was either aq0aq or aq1aq,
where aq0aq meant "ignore".
The second character denoted the terminal: aq8aq stood for "/dev/tty8".
The third character was an argument to
getty(8)
indicating the sequence of line speeds to try (aq-aq was: start trying
110 baud).
Thus a typical line was "18-".
A hang on some line was solved by changing the aq1aq to a aq0aq,
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 (aq0aq was: cycle through
300-1200-150-110 baud; aq4aq 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.
CONFORMING TO
SUSv1; marked as LEGACY 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
/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.
This page is part of release 3.14 of the Linux
man-pages
project.
A description of the project,
and information about reporting bugs,
can be found at
http://www.kernel.org/doc/man-pages/.
