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SOCKETPAIR(2) System Calls Manual SOCKETPAIR(2)

socketpair
create a pair of connected sockets

#include <sys/socket.h>
int
socketpair(int domain, int type, int protocol, int sv[2]);

The socketpair() call creates an unnamed pair of connected sockets. The descriptors used in referencing the new sockets are returned in sv[0] and sv[1]. The two sockets are indistinguishable.
The only supported domain is AF_UNIX. Possible values for the type and protocol arguments are explained in the socket(2) manual page. The only useful value for protocol is 0, which will let the system select an appropriate protocol for the requested socket type.
Any combination of the following flags may additionally be used in the type argument:
SOCK_CLOEXEC
Set close-on-exec flag on both the new descriptors.
SOCK_NONBLOCK
Set non-blocking I/O mode on both the new sockets.

Upon successful completion, the value 0 is returned; otherwise the value -1 is returned and the global variable errno is set to indicate the error.

The call succeeds unless:
 
 
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The specified address family is not supported on this machine.
 
 
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The specified protocol is not supported on this machine.
 
 
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The specified protocol does not support creation of socket pairs.
 
 
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The combination of the specified protocol and type is not supported.
 
 
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The per-process descriptor table is full.
 
 
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The system file table is full.
 
 
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Insufficient resources were available in the system to perform the operation.
 
 
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The address sv does not specify a valid part of the process address space.

pipe(2), read(2), socket(2), write(2)

The socketpair() function conforms to IEEE Std 1003.1-2008 (“POSIX.1”). The SOCK_CLOEXEC and SOCK_NONBLOCK flags are expected to conform to a future revision of that standard.

The socketpair() function call appeared in 4.2BSD. Support for the SOCK_CLOEXEC and SOCK_NONBLOCK flags appeared in OpenBSD 5.7.
April 8, 2018 OpenBSD-current