1GETSOCKOPT(2) Linux Programmer's Manual GETSOCKOPT(2)
2
6 getsockopt, setsockopt - get and set options on sockets
7
9 #include <sys/types.h> /* See NOTES */
10 #include <sys/socket.h>
11 int getsockopt(int sockfd, int level, int optname,
13 void *optval, socklen_t *optlen);
14 int setsockopt(int sockfd, int level, int optname,
15 const void *optval, socklen_t optlen);
16
18 getsockopt() and setsockopt() manipulate options for the socket
19 referred to by the file descriptor sockfd. Options may exist at multi‐
20 ple protocol levels; they are always present at the uppermost socket
21 level.
22 When manipulating socket options, the level at which the option resides
24 and the name of the option must be specified. To manipulate options at
25 the sockets API level, level is specified as SOL_SOCKET. To manipulate
26 options at any other level the protocol number of the appropriate pro‐
27 tocol controlling the option is supplied. For example, to indicate
28 that an option is to be interpreted by the TCP protocol, level should
29 be set to the protocol number of TCP; see getprotoent(3).
30 The arguments optval and optlen are used to access option values for
32 setsockopt(). For getsockopt() they identify a buffer in which the
33 value for the requested option(s) are to be returned. For getsock‐
34 opt(), optlen is a value-result argument, initially containing the size
35 of the buffer pointed to by optval, and modified on return to indicate
36 the actual size of the value returned. If no option value is to be
37 supplied or returned, optval may be NULL.
38 Optname and any specified options are passed uninterpreted to the
40 appropriate protocol module for interpretation. The include file
41 <sys/socket.h> contains definitions for socket level options, described
42 below. Options at other protocol levels vary in format and name; con‐
43 sult the appropriate entries in section 4 of the manual.
44 Most socket-level options utilize an int argument for optval. For set‐
46 sockopt(), the argument should be nonzero to enable a boolean option,
47 or zero if the option is to be disabled.
48 For a description of the available socket options see socket(7) and the
50 appropriate protocol man pages.
51
53 On success, zero is returned for the standard options. On error, -1 is
54 returned, and errno is set appropriately.
55 Netfilter allows the programmer to define custom socket options with
57 associated handlers; for such options, the return value on success is
58 the value returned by the handler.
59
61 EBADF The argument sockfd is not a valid file descriptor.
62 EFAULT The address pointed to by optval is not in a valid part of
64 the process address space. For getsockopt(), this error may
65 also be returned if optlen is not in a valid part of the
66 process address space.
67 EINVAL optlen invalid in setsockopt(). In some cases this error can
69 also occur for an invalid value in optval (e.g., for the
70 IP_ADD_MEMBERSHIP option described in ip(7)).
71 ENOPROTOOPT
73 The option is unknown at the level indicated.
74 ENOTSOCK The file descriptor sockfd does not refer to a socket.
76
78 POSIX.1-2001, POSIX.1-2008, SVr4, 4.4BSD (these system calls first
79 appeared in 4.2BSD).
80
82 POSIX.1 does not require the inclusion of <sys/types.h>, and this
83 header file is not required on Linux. However, some historical (BSD)
84 implementations required this header file, and portable applications
85 are probably wise to include it.
86 For background on the socklen_t type, see accept(2).
88
90 Several of the socket options should be handled at lower levels of the
91 system.
92
94 ioctl(2), socket(2), getprotoent(3), protocols(5), ip(7), packet(7),
95 socket(7), tcp(7), udp(7), unix(7)
96
98 This page is part of release 4.15 of the Linux man-pages project. A
99 description of the project, information about reporting bugs, and the
100 latest version of this page, can be found at
101 https://www.kernel.org/doc/man-pages/.
102Linux 2017-09-15 GETSOCKOPT(2)