CONNECT(2) BSD System Calls Manual CONNECT(2)NAMEconnect — initiate a connection on a socket
Standard C Library (libc, -lc)
connect(int s, const struct sockaddr *name, socklen_t namelen);
The s argument is a socket. If it is of type SOCK_DGRAM, this call spec‐
ifies 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 communications space of
the socket. Each communications space interprets the name argument in
its own way. Generally, stream sockets may successfully 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.
The connect() function returns the value 0 if successful; otherwise the
value -1 is returned and the global variable errno is set to indicate the
The connect() system call fails if:
[EBADF] The s argument is not a valid descriptor.
[ENOTSOCK] The s argument is a descriptor for a file, not a
[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.
[ECONNREFUSED] The attempt to connect was forcefully rejected.
[ECONNRESET] The connection was reset by the remote host.
[ENETUNREACH] The network is not reachable from this host.
[EHOSTUNREACH] The remote host is not reachable from this host.
[EADDRINUSE] The address is already in use.
[EFAULT] The name argument 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)
for completion by selecting the socket for writing.
[EINTR] The connection attempt was interrupted by the delivery
of a signal. The connection will be established in
the background, as in the case of EINPROGRESS.
[EALREADY] A previous connection attempt has not yet been com‐
[EACCES] An attempt is made to connect to a broadcast address
(obtained through the INADDR_BROADCAST constant or the
INADDR_NONE return value) through a socket that does
not provide broadcast functionality.
[EAGAIN] An auto-assigned port number was requested but no
auto-assigned ports are available. Increasing the
port range specified by sysctl(3) MIB variables
net.inet.ip.portrange.last may alleviate the problem.
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 255 characters, or
an entire path name exceeded 1023 characters.
[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.
SEE ALSOaccept(2), getpeername(2), getsockname(2), select(2), socket(2),
The connect() system call appeared in 4.2BSD.
BSD September 5, 2010 BSD