| UNIX(4) |
AerieBSD 1.0 Refernce Manual |
UNIX(4) |
NAME
unix —
UNIX-domain protocol family
SYNOPSIS
#include <sys/types.h>
#include <sys/un.h>
DESCRIPTION
The
UNIX
protocol family is a collection of protocols
that provides local (on-machine) interprocess
communication through the normal
socket(2)
mechanisms.
The
UNIX
family supports the
SOCK_STREAM
and
SOCK_DGRAM
socket types and uses
filesystem pathnames for addressing.
ADDRESSING
UNIX
addresses are variable-length filesystem pathnames of
at most 104 characters.
The include file
‹sys/un.h›
defines this address:
struct sockaddr_un {
u_char sun_len;
u_char sun_family;
char sun_path[104];
};
Binding a name to a
UNIX
socket with
bind(2)
causes a socket file to be created in the filesystem.
This file is
not
removed when the socket is closed\(em\c
unlink(2)
must be used to remove the file.
The
UNIX
protocol family does not support broadcast addressing or any form
of
“wildcard”
matching on incoming messages.
All addresses are absolute- or relative-pathnames
of other
UNIX
sockets.
Normal filesystem access-control mechanisms are also
applied when referencing pathnames; e.g., the destination
of a
connect(2)
or
sendto(2)
must be writable.
PROTOCOLS
The
UNIX
protocol family is comprised of simple
transport protocols that support the
SOCK_STREAM
and
SOCK_DGRAM
abstractions.
SOCK_STREAM
sockets also support the communication of
.Ux
file descriptors through the use of the
msg_control
field in the
msg
argument to
sendmsg(2)
and
recvmsg(2).
Any valid descriptor may be sent in a message.
The file descriptor(s) to be passed are described using a
structcmsghdr
that is defined in the include file
‹sys/socket.h›.
The type of the message is
SCM_RIGHTS,
and the data portion of the messages is an array of integers
representing the file descriptors to be passed.
The number of descriptors being passed is defined
by the length field of the message;
the length field is the sum of the size of the header
plus the size of the array of file descriptors.
The received descriptor is a
duplicate
of the sender's descriptor, as if it were created with a call to
dup(2).
Per-process descriptor flags, set with
fcntl(2),
are
not
passed to a receiver.
Descriptors that are awaiting delivery, or that are
purposely not received, are automatically closed by the system
when the destination socket is closed.
SEE ALSO
socket(2),
netintro(4)
.Rs
.%T "An Introductory 4.3 BSD Interprocess Communication Tutorial"
.%B PS1
.%N 7
.Re
.Rs
.%T "An Advanced 4.3 BSD Interprocess Communication Tutorial"
.%B PS1
.%N 8
.Re
| AerieBSD 1.0 Reference Manual |
August 26 2008 |
UNIX(4) |