Does anyone know how to check the current value of initcwnd? (particularly on Debian [Squeeze])

I've searched, but can't find a definitive answer to this. I haven't changed it, but may want to depending on it's current setting.


Get the source code of your running kernel and inspect include/net/tcp.h. There you will find:

/* TCP initial congestion window */
#define TCP_INIT_CWND 10

This being the default value, and rarely changed even in userland, it isn't otherwise exposed.

  • Ok thanks - I'll try to get the source, although this is a custom build for a Xen VPS. A pity it's not exposed to the users. Thanks for providing a definitive answer though. – UpTheCreek Nov 4 '14 at 15:38
  • Ah, indeed it was 10 :) – UpTheCreek Nov 4 '14 at 16:42

According to CDN planet, you would find it by typing

ip route show

Maybe this assumes that you have changed it yourself first.

  • Yes, that only shows the value if you have changed it yourself unfortunately. I'm looking for a way of finding the current value regardless of whether or not it was changed. – UpTheCreek Nov 4 '14 at 10:05
  • According to kernel newbies it is set to 10 per default, if you use kernel 2.6.39 or later. – mattias Nov 4 '14 at 10:12
  • Thanks. Still would like to be able to verify though. – UpTheCreek Nov 4 '14 at 10:14

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