getsockopt(2) — Linux manual page

NAME \| LIBRARY \| SYNOPSIS \| DESCRIPTION \| RETURN VALUE \| ERRORS \| STANDARDS \| HISTORY \| BUGS \| SEE ALSO \| COLOPHON

 getsockopt(2)              System Calls Manual              getsockopt(2)

NAME top

        getsockopt, setsockopt - get and set options on sockets

LIBRARY top

        Standard C library (libc, -lc)

SYNOPSIS top

        #include <sys/socket.h>         int getsockopt(socklen *restrict optlen;                       int sockfd, int level, int optname,                       void optval[_Nullable restrict *optlen],                       socklen_t *restrict optlen);        int setsockopt(socklen_t optlen;                       int sockfd, int level, int optname,                       const void optval[optlen],                       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 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.

RETURN VALUE top

        On success, zero is returned for the standard options.  On error,        -1 is returned, and errno is set to indicate the error.         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)).         ENOPROTOOPT               The option is unknown at the level indicated.         ENOTSOCK               The file descriptor sockfd does not refer to a socket.

STANDARDS top

        POSIX.1-2008.

HISTORY top

        POSIX.1-2001, SVr4, 4.4BSD (first appeared in 4.2BSD).

BUGS top

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

COLOPHON top

        This page is part of the man-pages (Linux kernel and C library        user-space interface documentation) project.  Information about        the project can be found at         ⟨https://www.kernel.org/doc/man-pages/⟩.  If you have a bug report        for this manual page, see        ⟨https://git.kernel.org/pub/scm/docs/man-pages/man-pages.git/tree/CONTRIBUTING⟩.        This page was obtained from the tarball man-pages-6.15.tar.gz        fetched from        ⟨https://mirrors.edge.kernel.org/pub/linux/docs/man-pages/⟩ on        2025-08-11.  If you discover any rendering problems in this HTML        version of the page, or you believe there is a better or more up-        to-date source for the page, or you have corrections or        improvements to the information in this COLOPHON (which is not        part of the original manual page), send a mail to        [email protected]  Linux man-pages 6.15            2025-06-28                  getsockopt(2)

Pages that refer to this page: connect(2), PR_SET_TAGGED_ADDR_CTRL(2const), recv(2), send(2), socket(2), socketcall(2), syscalls(2), if_nameindex(3), io_uring_prep_cmd(3), sctp_connectx(3), sockaddr(3type), 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)