getsockopt(2) — Linux manual page


GETSOCKOPT(2)             Linux Programmer's Manual            GETSOCKOPT(2)

NAME         top

       getsockopt, setsockopt - get and set options on sockets

SYNOPSIS         top

       #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);

DESCRIPTION         top

       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

       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.

RETURN VALUE         top

       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.

ERRORS         top

       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)).

              The option is unknown at the level indicated.

              The file descriptor sockfd does not refer to a socket.

CONFORMING TO         top

       POSIX.1-2001, POSIX.1-2008, SVr4, 4.4BSD (these system calls first
       appeared in 4.2BSD).

NOTES         top

       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).

BUGS         top

       Several of the socket options should be handled at lower levels of
       the system.

SEE ALSO         top

       ioctl(2), socket(2), getprotoent(3), protocols(5), ip(7), packet(7),
       socket(7), tcp(7), udp(7), unix(7)

COLOPHON         top

       This page is part of release 5.08 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

Linux                            2020-04-11                    GETSOCKOPT(2)

Pages that refer to this page: connect(2)recv(2)recvfrom(2)recvmsg(2)send(2)sendmsg(2)sendto(2)socket(2)socketcall(2)syscalls(2)if_freenameindex(3)if_nameindex(3)sctp_connectx(3)bpf-helpers(7)BPF-HELPERS(7)ip(7)ipv6(7)netlink(7)raw(7)sctp(7)signal-safety(7)socket(7)tcp(7)udp(7)udplite(7)unix(7)vsock(7)x25(7)