sys_un (0p) - Linux Manuals

sys_un: definitions for UNIX domain sockets


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.


sys/un.h --- definitions for UNIX domain sockets


#include <sys/un.h>


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.


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).






Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 7, Copyright (C) 2013 by the Institute of Electrical and Electronics Engineers, Inc and The Open Group. (This is POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) 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 .

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 .



The System Interfaces volume of POSIX.1-2008, bind(), socket(), socketpair()