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 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. Each communications space interprets the
name parameter in its own way. Generally, stream sockets may success‐
fully 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() call fails if:
[EBADF] s is not a valid descriptor.
[ENOTSOCK] s is a descriptor for a file, 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.
[ECONNREFUSED] The attempt to connect was forcefully rejected.
[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 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)
for completion by selecting the socket for writing.
[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 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)HISTORY
The connect() function call appeared in 4.2BSD.
BSD June 4, 1993 BSD