1CONNECT(2) Linux Programmer's Manual CONNECT(2)
2
6 connect - initiate a connection on a socket
7
9 #include <sys/types.h>
10 #include <sys/socket.h>
11 int connect(int sockfd, const struct sockaddr *serv_addr, socklen_t
13 addrlen);
14
16 The connect() system call connects the socket referred to by the file
17 descriptor sockfd to the address specified by serv_addr. The addrlen
18 argument specifies the size of serv_addr. The format of the address in
19 serv_addr is determined by the address space of the socket sockfd; see
20 socket(2) for further details.
21 If the socket sockfd is of type SOCK_DGRAM then serv_addr is the
23 address to which datagrams are sent by default, and the only address
24 from which datagrams are received. If the socket is of type
25 SOCK_STREAM or SOCK_SEQPACKET, this call attempts to make a connection
26 to the socket that is bound to the address specified by serv_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.
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(2).)
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 EAGAIN No more free local ports or insufficient entries in the routing
60 cache. For PF_INET see the net.ipv4.ip_local_port_range sysctl
61 in ip(7) on how to increase the number of local ports.
62 EALREADY
64 The socket is non-blocking 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 non-blocking and the connection cannot be com‐
78 pleted immediately. It is possible to select(2) or poll(2) for
79 completion by selecting the socket for writing. After select(2)
80 indicates writability, use getsockopt(2) to read the SO_ERROR
81 option at level SOL_SOCKET to determine whether connect() com‐
82 pleted successfully (SO_ERROR is zero) or unsuccessfully
83 (SO_ERROR is one of the usual error codes listed here, explain‐
84 ing the reason for the failure).
85 EINTR The system call was interrupted by a signal that was caught.
87 EISCONN
89 The socket is already connected.
90 ENETUNREACH
92 Network is unreachable.
93 ENOTSOCK
95 The file descriptor is not associated with a socket.
96 ETIMEDOUT
98 Timeout while attempting connection. The server may be too busy
99 to accept new connections. Note that for IP sockets the timeout
100 may be very long when syncookies are enabled on the server.
101
103 SVr4, 4.4BSD, (the connect() function first appeared in 4.2BSD),
104 POSIX.1-2001.
105
107 The third argument of connect() is in reality an int (and this is what
108 4.x BSD and libc4 and libc5 have). Some POSIX confusion resulted in
109 the present socklen_t, also used by glibc. See also accept(2).
110
112 Unconnecting a socket by calling connect() with a AF_UNSPEC address is
113 not yet implemented.
114
116 accept(2), bind(2), getsockname(2), listen(2), path_resolution(2),
117 socket(2)
118Linux 2.6.7 2004-06-23 CONNECT(2)