How to view/change socket connection timeout on Linux?

Question

When creating a Socket in Java:

new Socket(host, port);

The Socket constructor will try to connect to host:port before returning. On Windows, this fails almost immediately for unreachable hosts but for Linux it can take up to 5 minutes for the Socket to timeout.

I'm aware that if I have control over creating the Sockets, I can do:

Socket s = new Socket();
s.bind(..);
s.connect(.., timeout);

but I'd rather have the OS use a reasonable default value. Is there a way to change this setting on Linux?

Thanks

Answer 1

It's my understanding that this depends on the system's TCP/IP default timeout (240 seconds by default?)... one option is to try tweaking those, however this could affect any other programs on the same machine which rely on the timeout value. In which case, it might be safer to simply lower the "timeout" value in your Java connect() call, instead.

Answer 2

I think you want /proc/sys/net/ipv4/tcp-syn-retries. The default is usually 5 or 6 which comes out to around 3 minutes.

Note that these are system-wide.

Answer 3

I would advise against changing OS settings as it might affect other applications unexpectedly. The Socket.setSoTimeout() method might help you too.