How to know if remote TCP device is down?
By default, TCP blocking socket will block when remote TCP device is down. We can use TCP KEEPALIVE to check:
setsockopt(SOL_SOCKET, SO_KEEPALIVE,...);
and set the TCP keep alive settings:
sysctl -w net.ipv4.tcp_keepalive_intvl = 10
sysctl -w net.ipv4.tcp_keepalive_time = 30
sysctl -w net.ipv4.tcp_keepalive_probes = 2
Then, the socket recv() function will return -1 when remote device is down.
