--- name: "connect" section: "2" platform: "freebsd" package: "base" version: "16.0-CURRENT-20261027-61c70dc16a79" release: "FreeBSD 16.0-CURRENT (2026-10-27)" platforms: ["linux", "freebsd", "macos"] url: "https://new.carta.tech/connect/2" --- # connect(2) initiate a connection on a socket ## NAME **connect** – initiate a connection on a socket ## LIBRARY Standard C Library (libc, -lc) ## SYNOPSIS **#include \** *int*\ **connect**(*int s*, *const struct sockaddr \*name*, *socklen\_t namelen*); ## DESCRIPTION The *s* argument 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 communications space of the socket. *namelen* indicates the amount of space pointed to by *name*, in bytes; the *sa\_len* member of *name* is ignored. 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. ## RETURN VALUES 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 error. ## ERRORS The **connect**() system call fails if: - \[EBADF\] The *s* argument is not a valid descriptor. - \[EINVAL\] The *namelen* argument is not a valid length for the address family. - \[ENOTSOCK\] The *s* argument is a descriptor for a file, not a socket. - \[EADDRNOTAVAIL\] The specified address is not available on this machine. - \[EAFNOSUPPORT\] Addresses in the specified address family cannot be used with this socket. - \[EISCONN\] The socket is already connected. - \[ETIMEDOUT\] Connection establishment timed out without establishing 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)](/select/2.md) 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 completed. - \[EACCES\] 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)](/sysctl/3.md) MIB variables *net.inet.ip.portrange.first* and *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 path prefix. - \[EACCES\] Write access to the named socket is denied. - \[ELOOP\] Too many symbolic links were encountered in translating the pathname. - \[EPERM\] Write access to the named socket is denied. ## SEE ALSO [accept(2)](/accept/2.md), [getpeername(2)](/getpeername/2.md), [getsockname(2)](/getsockname/2.md), [select(2)](/select/2.md), [socket(2)](/socket/2.md), [sysctl(3)](/sysctl/3.md), [sysctl(8)](/sysctl/8.md) ## HISTORY The **connect**() system call appeared in 4.2BSD.