2.9BSD/usr/man/man5/ttys.5

.TH TTYS 5 
.UC
.SH NAME
ttys \- terminal initialization data
.SH DESCRIPTION
The
.I ttys
file is read by the
.I init
program and specifies
which terminal special files are to have
a process created for them which will allow people to
log in.
It contains one line per special file.
.PP
The first character of a line controls when it will be used.
A '0' or '1' indicates that the line is to be off or on, respectively.
A '2' or '3' means that the line will be used in "special session";
see
.IR init (8).
If the character is a '3', it will also be used for normal multi-user
operations.
The second character is used as an argument to
.IR getty (8),
which performs such tasks as baud-rate recognition,
reading the login name,
and calling
.IR login (1).
For normal lines,
the character is `0';
other characters can be used, for example, with hard-wired terminals
where speed recognition is unnecessary
or which have special characteristics.
.RI ( getty
will have to be fixed in such cases.)
The  next field of the line is the terminal's entry
in the device directory, /dev.
This field is terminated by a whitespace character. 
The rest of the line is optional information in the form of
terminal type (as found in /etc/termcap), port type and number
(e.g. `dh', `0'), and remarks (room number, nearby phone, dialup number, etc).
.SH FILES
/etc/ttys
.SH "SEE ALSO"
login(1), init(8), getty(8)