TTYSLOT(3)						     Linux Programmer's Manual							TTYSLOT(3)

NAME

       ttyslot - find the slot of the current user's terminal in some file

SYNOPSIS

       #include <unistd.h>    /* on BSD-like systems  */
       #include <stdlib.h>    /* on SYSV-like systems */

       int ttyslot(void);

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(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', signalling  init,
       changing back again, and signalling 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.  SYSV-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 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 current process in the file /etc/ttys, and that is (usu-
       ally) 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 SYSV-like  sys-
       tems 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  ter-
       minal that occurs in this data base) it returns 0 on Unix V6 and V7 and BSD-like systems, but -1 on SYSV-like systems.

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.

       Minix also has fttyslot(fd).

HISTORY

       ttyslot() appeared in Unix V7.

CONFORMS TO

       XPG2. Legacy in SUSv2. Deleted in SUSv3.  SUSv2 requires -1 on error.

SEE ALSO

       getttyent(3), ttyname(3), utmp(5)

GNU
								    2002-07-20								TTYSLOT(3)