1CONNECT(2) Linux Programmer's Manual CONNECT(2)
2
6 connect - initiate a connection on a socket
7
9 #include <sys/types.h> /* See NOTES */
10 #include <sys/socket.h>
11 int connect(int sockfd, const struct sockaddr *addr,
13 socklen_t addrlen);
14
16 The connect() system call connects the socket referred to by the file
17 descriptor sockfd to the address specified by addr. The addrlen argu‐
18 ment specifies the size of addr. The format of the address in addr is
19 determined by the address space of the socket sockfd; see socket(2) for
20 further details.
21 If the socket sockfd is of type SOCK_DGRAM then addr is the address to
23 which datagrams are sent by default, and the only address from which
24 datagrams are received. If the socket is of type SOCK_STREAM or
25 SOCK_SEQPACKET, this call attempts to make a connection to the socket
26 that is bound to the address specified by addr.
27 Generally, connection-based protocol sockets may successfully connect()
29 only once; connectionless protocol sockets may use connect() multiple
30 times to change their association. Connectionless sockets may dissolve
31 the association by connecting to an address with the sa_family member
32 of sockaddr set to AF_UNSPEC (supported on Linux since kernel 2.2).
33
35 If the connection or binding succeeds, zero is returned. On error, -1
36 is returned, and errno is set appropriately.
37
39 The following are general socket errors only. There may be other
40 domain-specific error codes.
41 EACCES For UNIX domain sockets, which are identified by pathname: Write
43 permission is denied on the socket file, or search permission is
44 denied for one of the directories in the path prefix. (See also
45 path_resolution(7).)
46 EACCES, EPERM
48 The user tried to connect to a broadcast address without having
49 the socket broadcast flag enabled or the connection request
50 failed because of a local firewall rule.
51 EADDRINUSE
53 Local address is already in use.
54 EAFNOSUPPORT
56 The passed address didn't have the correct address family in its
57 sa_family field.
58 EADDRNOTAVAIL
60 Non-existent interface was requested or the requested address
61 was not local.
62 EALREADY
64 The socket is nonblocking and a previous connection attempt has
65 not yet been completed.
66 EBADF The file descriptor is not a valid index in the descriptor ta‐
68 ble.
69 ECONNREFUSED
71 No-one listening on the remote address.
72 EFAULT The socket structure address is outside the user's address
74 space.
75 EINPROGRESS
77 The socket is nonblocking and the connection cannot be completed
78 immediately. It is possible to select(2) or poll(2) for comple‐
79 tion by selecting the socket for writing. After select(2) indi‐
80 cates writability, use getsockopt(2) to read the SO_ERROR option
81 at level SOL_SOCKET to determine whether connect() completed
82 successfully (SO_ERROR is zero) or unsuccessfully (SO_ERROR is
83 one of the usual error codes listed here, explaining the reason
84 for the failure).
85 EINTR The system call was interrupted by a signal that was caught; see
87 signal(7).
88 EISCONN
90 The socket is already connected.
91 ENETUNREACH
93 Network is unreachable.
94 ENOTSOCK
96 The file descriptor is not associated with a socket.
97 ETIMEDOUT
99 Timeout while attempting connection. The server may be too busy
100 to accept new connections. Note that for IP sockets the timeout
101 may be very long when syncookies are enabled on the server.
102
104 SVr4, 4.4BSD, (the connect() function first appeared in 4.2BSD),
105 POSIX.1-2001.
106
108 POSIX.1-2001 does not require the inclusion of <sys/types.h>, and this
109 header file is not required on Linux. However, some historical (BSD)
110 implementations required this header file, and portable applications
111 are probably wise to include it.
112 The third argument of connect() is in reality an int (and this is what
114 4.x BSD and libc4 and libc5 have). Some POSIX confusion resulted in
115 the present socklen_t, also used by glibc. See also accept(2).
116
118 An example of the use of connect() is shown in getaddrinfo(3).
119
121 accept(2), bind(2), getsockname(2), listen(2), socket(2), path_resolu‐
122 tion(7)
123
125 This page is part of release 3.53 of the Linux man-pages project. A
126 description of the project, and information about reporting bugs, can
127 be found at http://www.kernel.org/doc/man-pages/.
128Linux 2008-12-03 CONNECT(2)