[erlang-questions] Difference in 'close' for gen_tcp recv vs. active

Jacob jacob01@REDACTED
Sun Apr 13 22:20:44 CEST 2014


On 13.04.2014 17:35, Dror Mein wrote:
> I had the same problem, but I thought using {keepalive,true} or
> {send_timeout,Time} would help. I see in wireshark that keep alive does
> not pass through but I still don't get an {error, closed}.
> Someone wrote that default timeout for keepalive is two hours. where can
> it be configured?

TCP keepalive configuration is OS dependant. What OS are you using?

NOTE: The following applies to _Linux_ :

With Linux you can either set it
  a) globally via sysctl net.ipv4.tcp_keepalive_*
  b) globally per /proc/sys/net/ipv4/tcp_keepalive_*
  c) per socket with setsockopt() and TCP_KEEPCNT, TCP_KEEPIDLE,
  d) per started (ELF) executable with the libkeepalive wrapper (see below).

see tcp(7) for details.

A helpful HOWTO can be found here:

ad d):
See the HOWTO above for details. I installed the libkeepalive0 package
(Ubuntu 13.10), tried it with Erlang (erts-6.0) and according to strace
it seems to work. I would avoid LD_PRELOAD hacks in production though.

The command line was
  LD_PRELOAD=libkeepalive.so KEEPCNT=20 KEEPIDLE=180 KEEPINTVL=60 erl

If you want to use strace to check what happens enter:
  LD_PRELOAD=libkeepalive.so KEEPCNT=20 KEEPIDLE=180 KEEPINTVL=60 strace
-f -o keep.str -e trace=setsockopt erl

and look into keep.str after using gen_tcp:connect/3.



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