EADDRINUSE
The specified local address is already in use or the
filesystem socket object already exists.
EBADF This error can occur for sendmsg(2) when sending a file
descriptor as ancillary data over a UNIX domain socket
(see the description of SCM_RIGHTS, above), and indicates
that the file descriptor number that is being sent is not
valid (e.g., it is not an open file descriptor).
ECONNREFUSED
The remote address specified by connect(2) was not a
listening socket. This error can also occur if the target
pathname is not a socket.
ECONNRESET
Remote socket was unexpectedly closed.
EFAULT User memory address was not valid.
EINVAL Invalid argument passed. A common cause is that the value
AF_UNIX was not specified in the sun_type field of passed
addresses, or the socket was in an invalid state for the
applied operation.
EISCONN
connect(2) called on an already connected socket or a
target address was specified on a connected socket.
ENOENT The pathname in the remote address specified to connect(2)
did not exist.
ENOMEM Out of memory.
ENOTCONN
Socket operation needs a target address, but the socket is
not connected.
EOPNOTSUPP
Stream operation called on non-stream oriented socket or
tried to use the out-of-band data option.
EPERM The sender passed invalid credentials in the struct ucred.
EPIPE Remote socket was closed on a stream socket. If enabled,
a SIGPIPE is sent as well. This can be avoided by passing
the MSG_NOSIGNAL flag to send(2) or sendmsg(2).
EPROTONOSUPPORT
Passed protocol is not AF_UNIX.
EPROTOTYPE
Remote socket does not match the local socket type
(SOCK_DGRAM versus SOCK_STREAM).
ESOCKTNOSUPPORT
Unknown socket type.
ESRCH While sending an ancillary message containing credentials
(SCM_CREDENTIALS), the caller specified a PID that does
not match any existing process.
ETOOMANYREFS
This error can occur for sendmsg(2) when sending a file
descriptor as ancillary data over a UNIX domain socket
(see the description of SCM_RIGHTS, above). It occurs if
the number of "in-flight" file descriptors exceeds the
RLIMIT_NOFILE resource limit and the caller does not have
the CAP_SYS_RESOURCE capability. An in-flight file
descriptor is one that has been sent using sendmsg(2) but
has not yet been accepted in the recipient process using
recvmsg(2).
This error is diagnosed since mainline Linux 4.5 (and in
some earlier kernel versions where the fix has been
backported). In earlier kernel versions, it was possible
to place an unlimited number of file descriptors in
flight, by sending each file descriptor with sendmsg(2)
and then closing the file descriptor so that it was not
accounted against the RLIMIT_NOFILE resource limit.
Other errors can be generated by the generic socket layer or by
the filesystem while generating a filesystem socket object. See
the appropriate manual pages for more information.
