PROLOG

       This  manual  page  is part of the POSIX Programmer's Manual.  The Linux implementation of this interface
       may differ (consult the corresponding Linux manual page for details of Linux behavior), or the  interface
       may not be implemented on Linux.

NAME

       sys/un.h — definitions for UNIX domain sockets

SYNOPSIS

       #include <sys/un.h>

DESCRIPTION

       The  <sys/un.h> header shall define the sockaddr_un structure, which shall include at least the following
       members:

           sa_family_t  sun_family  Address family.
           char         sun_path[]  Socket pathname.

       The sockaddr_un structure is used to store addresses for UNIX domain  sockets.   Pointers  to  this  type
       shall be cast by applications to struct sockaddr * for use with socket functions.

       The <sys/un.h> header shall define the sa_family_t type as described in <sys/socket.h>.

       The following sections are informative.

APPLICATION USAGE

       The size of sun_path has intentionally been left undefined. This is because different implementations use
       different  sizes.  For  example,  4.3  BSD uses a size of 108, and 4.4 BSD uses a size of 104. Since most
       implementations originate from BSD versions, the size is typically in the range 92 to 108.

       Applications  should  not  assume  a  particular  length  for  sun_path  or  assume  that  it  can   hold
       {_POSIX_PATH_MAX} bytes (256).

       Although  applications  are  required  to  initialize  all members (including any non-standard ones) of a
       sockaddr_in6 structure (see <netinet_in.h>), the same is not  required  for  the  sockaddr_un  structure,
       since  historically  many  applications only initialized the standard members. Despite this, applications
       are encouraged to initialize sockaddr_un structures in a manner similar to the required initialization of
       sockaddr_in6 structures.

RATIONALE

       None.

FUTURE DIRECTIONS

       None.

SEE ALSO

       <netinet_in.h>, <sys_socket.h>

       The System Interfaces volume of POSIX.1‐2017, bind(), socket(), socketpair()

COPYRIGHT

       Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1-2017, Standard
       for Information  Technology  --  Portable  Operating  System  Interface  (POSIX),  The  Open  Group  Base
       Specifications  Issue  7, 2018 Edition, Copyright (C) 2018 by the Institute of Electrical and Electronics
       Engineers, Inc and The Open Group.  In the event of any discrepancy between this version and the original
       IEEE and The Open Group Standard, the original IEEE and The Open Group Standard is the referee  document.
       The original Standard can be obtained online at http://www.opengroup.org/unix/online.html .

       Any  typographical  or formatting errors that appear in this page are most likely to have been introduced
       during  the  conversion  of  the  source  files  to  man  page  format.  To  report  such   errors,   see
       https://www.kernel.org/doc/man-pages/reporting_bugs.html .

IEEE/The Open Group                                   2017                                      sys_un.h(7POSIX)