NAME （名称）
getsockopt, setsockopt - get and set options on sockets
SYNOPSIS（概要）
#include <sys/types.h> /* See NOTES */
#include <sys/socket.h>
int getsockopt(int sockfd, int level, int optname, void *optval, socklen_t *optlen);
int setsockopt(int sockfd, int level, int optname, const void *optval, socklen_t optlen);
DESCRIPTION（描述）
getsockopt() and setsockopt() manipulate options for the socket referred to by the file descriptor sockfd. Options may exist at multiple protocol levels; they are always present at the uppermost socket level.
When manipulating socket options, the level at which the option resides and the name of the option must be specified. To manipulate options at the sockets API level, level is specified as SOL_SOCKET. To manipulate options at any other level the protocol number of the appropriate protocol controlling the option is supplied. For example, to indicate that an option is to be interpreted by the TCP protocol, level should be set to the protocol number of TCP; see getprotoent(3).
The arguments optval and optlen are used to access option values for setsockopt(). For getsockopt() they identify a buffer in which the value for the requested option(s) are to be returned. For getsockopt(), optlen is a value-result argument, initially containing the size of the buffer pointed to by optval, and modified on return to indicate the actual size of the value returned. If no option value is to be supplied or returned, optval may be NULL.
Optname and any specified options are passed uninterpreted to the appropriate protocol module for interpretation. The include file <sys/socket.h> contains definitions for socket level options, described below. Options at other protocol levels vary in format and name; consult the appropriate entries in section 4 of the manual.
Most socket-level options utilize an int argument for optval. For setsockopt(), the argument should be nonzero to enable a boolean option, or zero if the option is to be disabled.
For a description of the available socket options see socket(7) and the appropriate protocol man pages.
RETURN VALUE（返回值）
On success, zero is returned for the standard options. On error, -1 is returned, and errno is set appropriately.
Netfilter allows the programmer to define custom socket options with associated handlers; for such options, the return value on success is the value returned by the handler.
ERRORS（错误）
| ERRORS | English DESCRIPTION | 中文说明 |
|---|---|---|
| EBADF (Error: Bad Fd) | The argument sockfd is not a valid descriptor. | 无效的参数sockfd |
| EFAULT (Error: Fault) | The address pointed to by optval is not in a valid part of the process address space. For getsockopt(), this error may also be returned if optlen is not in a valid part of the process address space. | optval 指向的地址不在进程地址空间的有效部分。 对于函数 getsockopt()，如果指针参数 optlen 不在进程地址空间的有效部分中，也可能返回此错误。 |
| EINVAL (Error: invalid) | optlen invalid in setsockopt(). In some cases this error can also occur for an invalid value in optval (e.g., for the IP_ADD_MEMBERSHIP option described in ip(7)). | 在 setsockopt() 中 optlen 无效。 在某些情况下，optval 中的无效值也会发生此错误（例如，对于 ip(7) 中描述的 IP_ADD_MEMBERSHIP 选项）。 |
| ENOPROTOOPT (Error: No Protocol Option) | The option is unknown at the level indicated. | 在指定的 level 上，该 option 是未知的。 |
| ENOTSOCK | The file descriptor sockfd does not refer to a socket. | 输入的文件描述符sockfd并不是个套接字 |
CONFORMING TO（符合…）
POSIX.1-2001, POSIX.1-2008, SVr4, 4.4BSD (these system calls first appeared in 4.2BSD).
NOTES（说明）
POSIX.1 does not require the inclusion of <sys/types.h>, and this header file is not required on Linux. However, some historical (BSD) implementations required this header file, and portable applications are probably wise to include it.
The optlen argument of getsockopt() and setsockopt() is in reality an int [*] (and this is what 4.x BSD and libc4 and libc5 have). Some POSIX confusion resulted in the present socklen_t, also used by glibc. See also accept(2).
BUGS（缺陷）
Several of the socket options should be handled at lower levels of the system.
SEE ALSO（另见）
ioctl(2), socket(2), getprotoent(3), protocols(5), ip(7), packet(7), socket(7), tcp(7), udp(7), unix(7)
COLOPHON - Linux 2015-12-28
This page is part of release 4.04 of the Linux man-pages project. A description of the project, information about reporting bugs, and the latest version of this page, can be found at http://www.kernel.org/doc/man-pages/.
注：上述翻译是机翻加人工修正，可能还有不理解的地方导致翻译得不是很恰当；
