GETSOCKOPT (2)
get and set options on sockets
SYNOPSIS
#include <sys/types.h>
#include <sys/socket.h>
int getsockopt(int s , int level , int optname ,
void * optval , socklen_t * optlen );
int setsockopt(int s , int level , int optname ,
const void * optval , socklen_t optlen );
DESCRIPTION
Getsockopt
and
setsockopt
manipulate the
options
associated with a socket. Options may exist at multiple
protocol levels; they are always present at the uppermost
socket
level.
When manipulating socket options the level at which the
option resides and the name of the option must be specified.
To manipulate options at the socket level,
level
is specified as
SOL_SOCKET .
To manipulate options at any
other level the protocol number of the appropriate protocol
controlling the option is supplied. For example,
to indicate that an option is to be interpreted by the
TCP
protocol,
level
should be set to the protocol number of
TCP ;
see
getprotoent (3).
The parameters
optval
and
optlen
are used to access option values for
setsockopt .
For
getsockopt
they identify a buffer in which the value for the
requested option(s) are to be returned. For
getsockopt ,
optlen
is a value-result parameter, initially containing the
size of the buffer pointed to by
optval ,
and modified on return to indicate the actual size of
the value returned. If no option value is
to be supplied or returned,
optval
may be NULL.
Optname
and any specified options are passed uninterpreted to the appropriate
protocol module for interpretation. The include file
<sys/socket.h>
contains definitions for socket level options, described below. Options at
other protocol levels vary in format and name; consult the appropriate
entries in section 4 of the manual.
Most socket-level options utilize an
int
parameter for
optval .
For
setsockopt ,
the parameter should be non-zero to enable a boolean option, or zero if the
option is to be disabled.
For a description of the available socket options see
socket (7)
and the appropriate protocol man pages.
RETURN VALUE
On success, zero is returned. On error, -1 is returned, and
errno
is set appropriately.
ERRORS
EBADF
The argument
s
is not a valid descriptor.
ENOTSOCK
The argument
s
is a file, not a socket.
ENOPROTOOPT
The option is unknown at the level indicated.
EFAULT
The address pointed to by
optval
is not in a valid part of the process address space. For
getsockopt ,
this error may also be returned if
optlen
is not in a valid part of the process address space.
CONFORMING TO
SVr4, 4.4BSD (these system calls first appeared in 4.2BSD).
SVr4 documents additional ENOMEM and ENOSR error codes, but does
not document the
SO_SNDLOWAT , SO_RCVLOWAT , SO_SNDTIMEO , SO_RCVTIMEO
options
NOTE
The fifth argument of
getsockopt and setsockopt
is in reality an int [*] (and this is what BSD 4.* and libc4 and libc5 have).
Some POSIX confusion resulted in the present socklen_t.
The draft standard has not been adopted yet, but glibc2 already
follows it and also has socklen_t [*]. See also
accept (2).
BUGS
Several of the socket options should be handled at lower levels of the
system.
SEE ALSO
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