Main article: TCP connection
In-flight connections can happen on sockets which do not yet have a full established connection. For instance, when establishing a TCP connection using a three-way handshake, SYN and SYN-ACK have been exchanged but the final ACK is not send back to the server.
CRIU can handle the checkpoint of sockets in this state with the
--skip-in-flight option, which will ignore not yet completely established TCP connections. On restore the client is expected to handle the re-connection.