getsockopt(2)

1getsockopt(2)                 System Calls Manual                getsockopt(2)
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NAME

6       getsockopt, setsockopt - get and set options on sockets
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LIBRARY

9       Standard C library (libc, -lc)
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SYNOPSIS

12       #include <sys/socket.h>
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14       int getsockopt(int sockfd, int level, int optname,
15                      void optval[restrict *.optlen],
16                      socklen_t *restrict optlen);
17       int setsockopt(int sockfd, int level, int optname,
18                      const void optval[.optlen],
19                      socklen_t optlen);
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DESCRIPTION

22       getsockopt()  and  setsockopt()  manipulate  options for the socket re‐
23       ferred to by the file descriptor sockfd.  Options may exist at multiple
24       protocol levels; they are always present at the uppermost socket level.
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26       When manipulating socket options, the level at which the option resides
27       and the name of the option must be specified.  To manipulate options at
28       the sockets API level, level is specified as SOL_SOCKET.  To manipulate
29       options at any other level the protocol number of the appropriate  pro‐
30       tocol  controlling  the  option  is supplied.  For example, to indicate
31       that an option is to be interpreted by the TCP protocol,  level  should
32       be set to the protocol number of TCP; see getprotoent(3).
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34       The  arguments  optval  and optlen are used to access option values for
35       setsockopt().  For getsockopt() they identify a  buffer  in  which  the
36       value  for  the  requested  option(s) are to be returned.  For getsock‐
37       opt(), optlen is a value-result argument, initially containing the size
38       of  the buffer pointed to by optval, and modified on return to indicate
39       the actual size of the value returned.  If no option  value  is  to  be
40       supplied or returned, optval may be NULL.
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42       Optname  and  any specified options are passed uninterpreted to the ap‐
43       propriate  protocol  module  for  interpretation.   The  include   file
44       <sys/socket.h> contains definitions for socket level options, described
45       below.  Options at other protocol levels vary in format and name;  con‐
46       sult the appropriate entries in section 4 of the manual.
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48       Most socket-level options utilize an int argument for optval.  For set‐
49       sockopt(), the argument should be nonzero to enable a  boolean  option,
50       or zero if the option is to be disabled.
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52       For a description of the available socket options see socket(7) and the
53       appropriate protocol man pages.
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RETURN VALUE

56       On success, zero is returned for the standard options.  On error, -1 is
57       returned, and errno is set to indicate the error.
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59       Netfilter  allows  the  programmer to define custom socket options with
60       associated handlers; for such options, the return value on  success  is
61       the value returned by the handler.
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ERRORS

64       EBADF  The argument sockfd is not a valid file descriptor.
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66       EFAULT The  address  pointed to by optval is not in a valid part of the
67              process address space.  For getsockopt(), this error may also be
68              returned if optlen is not in a valid part of the process address
69              space.
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71       EINVAL optlen invalid in setsockopt().  In some cases  this  error  can
72              also  occur  for  an  invalid  value  in  optval  (e.g., for the
73              IP_ADD_MEMBERSHIP option described in ip(7)).
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75       ENOPROTOOPT
76              The option is unknown at the level indicated.
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78       ENOTSOCK
79              The file descriptor sockfd does not refer to a socket.
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STANDARDS

82       POSIX.1-2008.
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HISTORY

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

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