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NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | CONFORMING TO | NOTES | BUGS | SEE ALSO | COLOPHON |
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GETSOCKOPT(2) Linux Programmer's Manual GETSOCKOPT(2)
getsockopt, setsockopt - get and set options on sockets
#include <sys/types.h> /* See NOTES */
#include <sys/socket.h>
int getsockopt(int sockfd, int level, int optname,
void *optval, socklen_t *optlen);
int setsockopt(int sockfd, int level, int optname,
const void *optval, socklen_t optlen);
getsockopt() and setsockopt() manipulate options for the socket
referred to by the file descriptor sockfd. 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 sockets API 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 arguments 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 argument, 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 argument for optval.
For setsockopt(), the argument should be nonzero 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.
On success, zero is returned for the standard options. On error,
-1 is returned, and errno is set appropriately.
Netfilter allows the programmer to define custom socket options
with associated handlers; for such options, the return value on
success is the value returned by the handler.
EBADF The argument sockfd is not a valid file descriptor.
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(). In some cases this error
can also occur for an invalid value in optval (e.g., for
the IP_ADD_MEMBERSHIP option described in ip(7)).
ENOPROTOOPT
The option is unknown at the level indicated.
ENOTSOCK
The file descriptor sockfd does not refer to a socket.
POSIX.1-2001, POSIX.1-2008, SVr4, 4.4BSD (these system calls
first appeared in 4.2BSD).
POSIX.1 does not require the inclusion of <sys/types.h>, and this
header file is not required on Linux. However, some historical
(BSD) implementations required this header file, and portable
applications are probably wise to include it.
For background on the socklen_t type, see accept(2).
Several of the socket options should be handled at lower levels
of the system.
ioctl(2), socket(2), getprotoent(3), protocols(5), ip(7),
packet(7), socket(7), tcp(7), udp(7), unix(7)
This page is part of release 5.10 of the Linux man-pages project.
A description of the project, information about reporting bugs,
and the latest version of this page, can be found at
https://www.kernel.org/doc/man-pages/.
Linux 2020-04-11 GETSOCKOPT(2)
Pages that refer to this page: connect(2), prctl(2), recv(2), send(2), socket(2), socketcall(2), syscalls(2), if_nameindex(3), sctp_connectx(3), bpf-helpers(7), capabilities(7), ip(7), ipv6(7), netlink(7), packet(7), raw(7), sctp(7), signal(7), signal-safety(7), socket(7), tcp(7), udp(7), udplite(7), unix(7), vsock(7), x25(7)
Copyright and license for this manual page
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