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RHEL5.5 Socket Timeout Setting

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Operating Systems Linux Red Hat RHEL5.5 Socket Timeout Setting
# 1  
Old 10-08-2010
RHEL5.5 Socket Timeout Setting
Is there a Linux tunable to reduce the amount of time a socket waits before considering the remote side dead?
Its the same senario when you try to telnet to a dead machine, telnet sits and waits for ~30seconds, before the socket timer expires and cancels the request.
# 2  
Old 10-08-2010
TCP has such obnoxiously long timeouts because it's designed with best-effort delivery in mind. You'll find tunables in /proc/sys/net/ipv4 but beware, the rest of the internet won't change with them so altering them may have consequences beyond your intentions. Try pinging the host before you connect to it.
# 3  
Old 10-08-2010
These are the 3 relevant tunables:

Quote:
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.

tcp_keepalive_intvl

The interval between subsequential keepalive probes, regardless of what the connection has exchanged in the meantime.

tcp_keepalive_probes

The number of unacknowledged probes to send before considering the connection dead and notifying the application layer.
# 4  
Old 10-08-2010
Those tunables are only active/applicable if the app uses SO_KEEPALIVE() in the program, correct? unfortunately, our original developers didnt seem to think it was a necessary evil.
# 5  
Old 10-10-2010
Quote:
Originally Posted by mrmurdock
Those tunables are only active/applicable if the app uses SO_KEEPALIVE() in the program, correct? unfortunately, our original developers didnt seem to think it was a necessary evil.
If it's just one application you're worried about, I've had great success with libkeepalive, which uses libc preload tricks to enforce keepalive options in new sockets by default. (do NOT have it preloaded globally. That way lies madness.) You'd be severely perverting its design intentions in making connections die faster though! Smilie
Last edited by Corona688; 10-10-2010 at 02:55 AM..
# 6  
Old 10-10-2010
Quote:
Those tunables are only active/applicable if the app uses SO_KEEPALIVE() in the program, correct?
Correct. As far as I recall, keepalive support is not the default behavior in GNU/Linux. Apps must request keepalive using the setsockopt interface.
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