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>.
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>
XSH bind(3), socket(3), socketpair(3)
CHANGE HISTORY
First released in Issue 6. Derived from the XNS, Issue 5.2 specification.
Issue 7
The value for {_POSIX_PATH_MAX} is updated to 256.
POSIX.1-2008, Technical Corrigendum 1, XBD/TC1-2008/0074 [355] is applied.
POSIX.1-2008, Technical Corrigendum 2, XBD/TC2-2008/0081 [934] is applied.