CONNECT(2) BSD System Calls Manual CONNECT(2)
connect -- initiate a connection on a socket
connect(int s, const struct sockaddr *name, socklen_t namelen);
The parameter s is a socket. If it is of type SOCK_DGRAM, this call
specifies the peer with which the socket is to be associated; this
address is that to which datagrams are to be sent, and the only address
from which datagrams are to be received. If the socket is of type
SOCK_STREAM, this call attempts to make a connection to another socket.
The other socket is specified by name, which is an address in the commu-
nications space of the socket. namelen indicates the amount of space
pointed to by name, in bytes. Each communications space interprets the
name parameter in its own way. Generally, stream sockets may use
connect() only once; datagram sockets may use connect() multiple times to
change their association. Datagram sockets may dissolve the association
by connecting to an invalid address, such as a null address.
If the connection or binding succeeds, 0 is returned. Otherwise a -1 is
returned, and a more specific error code is stored in errno.
The connect() call fails if:
[EBADF] s is not a valid descriptor.
[ENOTSOCK] s is not a socket.
[EADDRNOTAVAIL] The specified address is not available on this
[EAFNOSUPPORT] Addresses in the specified address family cannot be
used with this socket.
[EISCONN] The socket is already connected.
[ETIMEDOUT] Connection establishment timed out without establish-
ing a connection.
[EINVAL] A TCP connection with a local broadcast, the all-ones
or a multicast address as the peer was attempted.
[ECONNREFUSED] The attempt to connect was forcefully rejected.
[EHOSTUNREACH] The destination address specified an unreachable host.
[EINTR] A connect was interrupted before it succeeded by the
delivery of a signal.
[ENETUNREACH] The network isn't reachable from this host.
[EADDRINUSE] The address is already in use.
[EFAULT] The name parameter specifies an area outside the
process address space.
[EINPROGRESS] The socket is non-blocking and the connection cannot
be completed immediately. It is possible to select(2)
or poll(2) for completion by selecting the socket for
writing, and also use getsockopt(2) with SO_ERROR to
check for error conditions.
[EALREADY] The socket is non-blocking and a previous connection
attempt has not yet been completed.
The following errors are specific to connecting names in the UNIX-domain.
These errors may not apply in future versions of the UNIX IPC domain.
[ENOTDIR] A component of the path prefix is not a directory.
[ENAMETOOLONG] A component of a pathname exceeded NAME_MAX charac-
ters, or an entire pathname (including the terminating
NUL) exceeded PATH_MAX bytes.
[ENOENT] The named socket does not exist.
[EACCES] Search permission is denied for a component of the
[EACCES] Write access to the named socket is denied.
[ELOOP] Too many symbolic links were encountered in translat-
ing the pathname.
[EPROTOTYPE] The file described by name is of a different type than
s. E.g., s may be of type SOCK_STREAM whereas name
may refer to a socket of type SOCK_DGRAM.
accept(2), getsockname(2), getsockopt(2), poll(2), select(2), socket(2)
The connect() function conforms to IEEE Std 1003.1-2008 (``POSIX.1'').
The connect() system call first appeared in 4.1cBSD.
BSD April 28, 2017 BSD