$cat /proc/sys/net/ipv4/tcp_keepalive_time 7200 $
tcp_keepalive_time the interval between the last data packet sent (simple ACKs are not considered data) and the first keepalive probe; after the connection is marked to need keepalive, this counter is not used any further source :http://tldp.org/HOWTO/TCP-Keepalive-HOWTO/usingkeepalive.html
linux/net/ipv4/tcp.c - 8 identical 365: * TCP Keep-Alives (4.2.3.6) 366: * MAY provide keep-alives. (does) 367: * MUST make keep-alives configurable on a per-connection basis. (does) 1863: * problem with TCP as specified in that the other end could 1864: * keep a socket open forever with no application left this end. 1865: * We use a 3 minute timeout (about the same as BSD) then kill ftp.kernel.org/pub/linux/kernel/v2.4/linux-2.4.0.tar.bz2 - GPL - C -
The TCP specification states that if keep-alive is provided, by default keep-alivemust be turned off and the threshold time before which a keep-alive is sent must be 7200 seconds or more (inter keep-alive time should also be 7200 seconds). source : Research Related Paper. http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.55.4690&rep=rep1&type=pdf