MsgFlags

No flags defined

Sends out-of-band data on sockets that support this notion (e.g., of type SOCK_STREAM); the underlying protocol must also support out-of-band data.

This flag causes the receive operation to return data from the beginning of the receive queue without removing that data from the queue. Thus, a subsequent receive call will return the same data.

Don't use a gateway to send out the packet, send to hosts only on directly connected networks. This is usually used only by diagnostic or routing programs. This is defined only for protocol families that route; packet sockets don't.

For raw (AF_PACKET), Internet datagram (since Linux 2.4.27/2.6.8), netlink (since Linux 2.6.22), and UNIX datagram (since Linux 3.4) sockets: return the real length of the packet or datagram, even when it was longer than the passed buffer.

For use with Internet stream sockets, see tcp(7).

Enables nonblocking operation; if the operation would block, EAGAIN or EWOULDBLOCK is returned. This provides similar behavior to setting the O_NONBLOCK flag (via the fcntl(2) F_SETFL operation), but differs in that MSG_DONTWAIT is a per-call option, whereas O_NONBLOCK is a setting on the open file description (see open(2)), which will affect all threads in the calling process and as well as other processes that hold file descriptors referring to the same open file description.

Terminates a record (when this notion is supported, as for sockets of type SOCK_SEQPACKET).

This flag requests that the operation block until the full request is satisfied. However, the call may still return less data than requested if a signal is caught, an error or disconnect occurs, or the next data to be received is of a different type than that returned. This flag has no effect for datagram sockets.

Tell the link layer that forward progress happened: you got a successful reply from the other side. If the link layer doesn't get this it will regularly reprobe the neighbor (e.g., via a unicast ARP). Valid only on SOCK_DGRAM and SOCK_RAW sockets and currently implemented only for IPv4 and IPv6. See arp(7) for details.

This flag specifies that queued errors should be received from the socket error queue. The error is passed in an ancillary message with a type dependent on the protocol (for IPv4 IP_RECVERR). The user should supply a buffer of sufficient size. See cmsg(3) and ip(7) for more information. The payload of the original packet that caused the error is passed as normal data via msg_iovec. The original destination address of the datagram that caused the error is supplied via msg_name.

Don't generate a SIGPIPE signal if the peer on a stream-oriented socket has closed the connection. The EPIPE error is still returned. This provides similar behavior to using sigaction(2) to ignore SIGPIPE, but, whereas MSG_NOSIGNAL is a per-call feature, ignoring SIGPIPE sets a process attribute that affects all threads in the process.

The caller has more data to send. This flag is used with TCP sockets to obtain the same effect as the TCP_CORK socket option (see tcp(7)), with the difference that this flag can be set on a per-call basis.

Since Linux 2.6, this flag is also supported for UDP sockets, and informs the kernel to package all of the data sent in calls with this flag set into a single datagram which is transmitted only when a call is performed that does not specify this flag.

See_Also: the UDP_CORK socket option described in udp(7)

Set the close-on-exec flag for the file descriptor received via a UNIX domain file descriptor using the SCM_RIGHTS operation (described in unix(7)). This flag is useful for the same reasons as the O_CLOEXEC flag of open(2). (recvmsg only)