How can I detect a TCP connection in linux in C?

Question

I wrote a program in C where the client sent some information once to the server. I used TCP sockets. And for some time the server calculated and had to send the result to the client. How can I detect that the connection on the server or client has been broken?

Answer 1

You can try TCP keepalives.

  # cat /proc/sys/net/ipv4/tcp_keepalive_time
  7200

  # cat /proc/sys/net/ipv4/tcp_keepalive_intvl
  75

  # cat /proc/sys/net/ipv4/tcp_keepalive_probes
  9`

In the above example, the TCP continue timer starts after 7200 seconds of inactivity. If keep-alive messages are unsuccessful, they are repeated at intervals of 75 seconds. After 9 consecutive attempts to reconnect, the connection will be disconnected.

keepalive , script /etc/init.d.

Answer 2

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Answer 3

TCP Keep-Alive - , ​​. , TCP-.

http://tldp.org/HOWTO/TCP-Keepalive-HOWTO/overview.html

, tcp keep-alives (SO_KEEPALIVE) setsockopt.

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Answer 4

Linux :

1. (uint) .
2. readlinkfile /proc/[pid]/fd/[#hander]. If it is a socket, it will return a type string socket:[#inode].
3. Read /proc/net/tcp, find the row with this index (11th column).
4. Read the status column ( st) in this row (4th column). If it is 0x07 (Close) or 0x08 (TIME_WAIT), the socket is dead.