GETSOCKOPT(3POSIX)

PROLOG
This manual page is part of the POSIX Programmer's Manual. The Linux implementation of this interface may differ (consult the corresponding Linux manual page for details of Linux behavior), or the interface may not be implemented on Linux.

NAME
getsockopt — get the socket options

SYNOPSIS

#include <sys/socket.h>

int getsockopt(int socket, int level, int option_name,
    void *restrict option_value, socklen_t *restrict option_len);

DESCRIPTION
The getsockopt() function manipulates options associated with a socket.

The getsockopt() function shall retrieve the value for the option specified by the option_name argument for the socket specified by the socket argument. If the size of the option value is greater than option_len, the value stored in the object pointed to by the option_value argument shall be silently truncated. Otherwise, the object pointed to by the option_len argument shall be modified to indicate the actual length of the value.

The level argument specifies the protocol level at which the option resides. To retrieve options at the socket level, specify the level argument as SOL_SOCKET. To retrieve options at other levels, supply the appropriate level identifier for the protocol controlling the option. For example, to indicate that an option is interpreted by the TCP (Transmission Control Protocol), set level to IPPROTO_TCP as defined in the <netinet/in.h> header.

The socket in use may require the process to have appropriate privileges to use the getsockopt() function.

The option_name argument specifies a single option to be retrieved. It can be one of the socket-level options defined in <sys_socket.h> and described in Section 2.10.16, Use of Options.

RETURN VALUE
Upon successful completion, getsockopt() shall return 0; otherwise, -1 shall be returned and errno set to indicate the error.

ERRORS
The getsockopt() function shall fail if:

EBADF
    The socket argument is not a valid file descriptor.

EINVAL
    The specified option is invalid at the specified socket level.

ENOPROTOOPT
    The option is not supported by the protocol.

ENOTSOCK
    The socket argument does not refer to a socket.

The getsockopt() function may fail if:

EACCES
    The calling process does not have appropriate privileges.

EINVAL
    The socket has been shut down.

ENOBUFS
    Insufficient resources are available in the system to complete the function.

The following sections are informative.

EXAMPLES
None.

APPLICATION USAGE
None.

RATIONALE
None.

FUTURE DIRECTIONS
None.

SEE ALSO
Section 2.10.16, Use of Options, bind(), close(), endprotoent(), setsockopt(), socket()

The Base Definitions volume of POSIX.1-2017, <sys_socket.h>, <netinet_in.h>

COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1-2017, Standard for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 7, 2018 Edition, Copyright (C) 2018 by the Institute of Electrical and Electronics Engineers, Inc and The Open Group. In the event of any discrepancy between this version and the original IEEE and The Open Group Standard, the original IEEE and The Open Group Standard is the referee document. The original Standard can be obtained online at http://www.opengroup.org/unix/online.html .

Any typographical or formatting errors that appear in this page are most likely to have been introduced during the conversion of the source files to man page format. To report such errors, see https://www.kernel.org/doc/man-pages/reporting_bugs.html .