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, and Linux */
       #include <stdlib.h>    /* on System V-like systems */

       int ttyslot(void);

   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

       ttyslot(): _BSD_SOURCE || (_XOPEN_SOURCE_EXTENDED && ! _XOPEN_SOURCE >= 500)

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 ter-
       minal 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(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 asso-
       ciated with a terminal that occurs in this data base) it returns 0 on Unix V6 and V7 and BSD-like systems, but -1 on Sys-
       tem 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.

       Minix also has fttyslot(fd).

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

COLOPHON
       This page is part of release 3.25 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/.



GNU                                                        2007-11-26                                                 TTYSLOT(3)