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.\"     @(#)getpeername.2	6.5 (Berkeley) 3/10/91
.\"
.\" Modified Sat Jul 24 16:37:50 1993 by Rik Faith <faith@cs.unc.edu>
.\" Modified Thu Jul 30 14:37:50 1993 by Martin Schulze <joey@debian.org>
.\" Modified Sun Mar 28 21:26:46 1999 by Andries Brouwer <aeb@cwi.nl>
.\" Modified 17 Jul 2002, Michael Kerrisk <mtk.manpages@gmail.com>
.\"	Added 'socket' to NAME, so that "man -k socket" will show this page.
.\"
.TH GETPEERNAME 2 2013-02-12 "Linux" "Linux Programmer's Manual"
.SH NAME
getpeername \- get name of connected peer socket
.SH SYNOPSIS
.B #include <sys/socket.h>
.sp
.BI "int getpeername(int " sockfd ", struct sockaddr *" addr \
", socklen_t *" addrlen );
.SH DESCRIPTION
.BR getpeername ()
returns the address of the peer connected to the socket
.IR sockfd ,
in the buffer pointed to by
.IR addr .
The
.I addrlen
argument should be initialized to indicate the amount of space pointed to
by
.IR addr .
On return it contains the actual size of the name returned (in bytes).
The name is truncated if the buffer provided is too small.

The returned address is truncated if the buffer provided is too small;
in this case,
.I addrlen
will return a value greater than was supplied to the call.
.SH RETURN VALUE
On success, zero is returned.
On error, \-1 is returned, and
.I errno
is set appropriately.
.SH ERRORS
.TP
.B EBADF
The argument
.I sockfd
is not a valid descriptor.
.TP
.B EFAULT
The
.I addr
argument points to memory not in a valid part of the
process address space.
.TP
.B EINVAL
.I addrlen
is invalid (e.g., is negative).
.TP
.B ENOBUFS
Insufficient resources were available in the system
to perform the operation.
.TP
.B ENOTCONN
The socket is not connected.
.TP
.B ENOTSOCK
The argument
.I sockfd
is a file, not a socket.
.SH CONFORMING TO
SVr4, 4.4BSD (the
.BR getpeername ()
function call first appeared in 4.2BSD), POSIX.1-2001.
.SH NOTES
The third argument of
.BR getpeername ()
is in reality an
.I int *
(and this is what 4.x BSD and libc4 and libc5 have).
Some POSIX confusion resulted in the present
.IR socklen_t ,
also used by glibc.
See also
.BR accept (2).

For stream sockets, once a
.BR connect (2)
has been performed, either socket can call
.BR getpeername ()
to obtain the address of the peer socket.
On the other hand, datagram sockets are connectionless.
Calling
.BR connect (2)
on a datagram socket merely sets the peer address for outgoing
datagrams sent with
.BR write (2)
or
.BR recv (2).
The caller of
.BR connect (2)
can use
.BR getpeername ()
to obtain the peer address that it earlier set for the socket.
However, the peer socket is unaware of this information, and calling
.BR getpeername ()
on the peer socket will return no useful information (unless a
.BR connect (2)
call was also executed on the peer).
Note also that the receiver of a datagram can obtain
the address of the sender when using
.BR recvfrom (2).
.SH SEE ALSO
.BR accept (2),
.BR bind (2),
.BR getsockname (2),
.BR ip (7),
.BR socket (7),
.BR unix (7)