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.
#include <sys/socket.h> int getsockopt(int socket, int level, int option_name, void *restrict option_value, socklen_t *restrict option_len);
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.
Upon successful completion, getsockopt() shall return 0; otherwise, -1 shall be returned and errno set to indicate the error.
The getsockopt() function shall fail if:
The socket argument is not a valid file descriptor.
The specified option is invalid at the specified socket level.
The option is not supported by the protocol.
The socket argument does not refer to a socket.
The getsockopt() function may fail if:
The calling process does not have appropriate privileges.
The socket has been shut down.
Insufficient resources are available in the system to complete the function.
The following sections are informative.
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>
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 .
if_freenameindex(3p), if_indextoname(3p), if_nameindex(3p), if_nametoindex(3p), netinet_in.h(0p), netinet_tcp.h(0p), send(3p), sendmsg(3p), sendto(3p), setsockopt(3p), shutdown(3p), socket(3p), sys_socket.h(0p).