1CONNECT(2)                 Linux Programmer's Manual                CONNECT(2)
2
3
4

NAME

6       connect - initiate a connection on a socket
7

SYNOPSIS

9       #include <sys/types.h>          /* See NOTES */
10       #include <sys/socket.h>
11
12       int connect(int sockfd, const struct sockaddr *addr,
13                   socklen_t addrlen);
14

DESCRIPTION

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
22       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
28       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

RETURN VALUE

35       If  the connection or binding succeeds, zero is returned.  On error, -1
36       is returned, and errno is set appropriately.
37

ERRORS

39       The following are general socket  errors  only.   There  may  be  other
40       domain-specific error codes.
41
42       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
47       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
52       EADDRINUSE
53              Local address is already in use.
54
55       EAFNOSUPPORT
56              The passed address didn't have the correct address family in its
57              sa_family field.
58
59       EADDRNOTAVAIL
60              Non-existent  interface  was  requested or the requested address
61              was not local.
62
63       EALREADY
64              The socket is nonblocking and a previous connection attempt  has
65              not yet been completed.
66
67       EBADF  The  file  descriptor is not a valid index in the descriptor ta‐
68              ble.
69
70       ECONNREFUSED
71              No-one listening on the remote address.
72
73       EFAULT The socket structure  address  is  outside  the  user's  address
74              space.
75
76       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
86       EINTR  The system call was interrupted by a signal that was caught; see
87              signal(7).
88
89       EISCONN
90              The socket is already connected.
91
92       ENETUNREACH
93              Network is unreachable.
94
95       ENOTSOCK
96              The file descriptor is not associated with a socket.
97
98       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

CONFORMING TO

104       SVr4,  4.4BSD,  (the  connect()  function  first  appeared  in 4.2BSD),
105       POSIX.1-2001.
106

NOTES

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
113       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

EXAMPLE

118       An example of the use of connect() is shown in getaddrinfo(3).
119

SEE ALSO

121       accept(2),  bind(2), getsockname(2), listen(2), socket(2), path_resolu‐
122       tion(7)
123

COLOPHON

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/.
128
129
130
131Linux                             2008-12-03                        CONNECT(2)
Impressum