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GETSOCKOPT(2) Linux Programmer’s Manual GETSOCKOPT(2)
NAME
getsockopt, setsockopt - 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 exam-
ple, 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 pro-
tocol module for interpretation. The include file <sys/socket.h> contains defini-
tions 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 man-
ual.
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 appropri-
ately.
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.
EINVAL optlen invalid in setsockopt
CONFORMING TO
SVr4, 4.4BSD (these system calls first appeared in 4.2BSD). SVr4 documents addi-
tional 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
ioctl(2), socket(2), getprotoent(3), protocols(5), socket(7), unix(7), tcp(7)
Linux Man Page 1999-05-24 GETSOCKOPT(2)
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