1GETSOCKOPT(2)              Linux Programmer's Manual             GETSOCKOPT(2)
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NAME

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

9       #include <sys/socket.h>
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11       int getsockopt(int sockfd, int level, int optname,
12                      void *restrict optval, socklen_t *restrict optlen);
13       int setsockopt(int sockfd, int level, int optname,
14                      const void *optval, socklen_t optlen);
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DESCRIPTION

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

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

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

77       POSIX.1-2001, POSIX.1-2008, SVr4, 4.4BSD (these system calls first  ap‐
78       peared in 4.2BSD).
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NOTES

81       For background on the socklen_t type, see accept(2).
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BUGS

84       Several  of the socket options should be handled at lower levels of the
85       system.
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SEE ALSO

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

92       This  page  is  part of release 5.13 of the Linux man-pages project.  A
93       description of the project, information about reporting bugs,  and  the
94       latest     version     of     this    page,    can    be    found    at
95       https://www.kernel.org/doc/man-pages/.
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99Linux                             2021-03-22                     GETSOCKOPT(2)
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