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



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

SYNOPSIS
       #include <&lt;unistd.h>&gt;    /* on BSD-like systems, and Linux */
       #include <&lt;stdlib.h>&gt;    /* 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 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 argu-
       ment 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 con-
       sole 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  cur-
       rently  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 (count-
       ing from 1).

   The semantics of ttyslot
       Thus, the function ttyslot() returns the index of the controlling  ter-
       minal  of  the calling 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 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 &lt;ttyent.h&gt; 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 3.05 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)