http://manpages.ubuntu.com/manpages/bionic/man7/tcp.7.html Here it states tcp_syn_retries is 5 by default. I haven't touched the defaults and I see 6 on my PC. I'm using Ubuntu 18.04.2 (did live upgrade from 16.04).
I also tried to report this bug via mail to linux-man@vger.kernel.org with cc to linux-man@vger.kernel.org, but got rejected as SPAM.
I did some more checks. Others also have 6 as default. This gives a timeout of around 128 seconds. And checking the retransmission algorithm with Wireshark, I guess a default of 5 would give a timeout of around 64 seconds.
Thanks for the report and further info. I applied the patch below. Closing this bug now. diff --git a/man7/tcp.7 b/man7/tcp.7 index 2c4c6f15a..5d950951b 100644 --- a/man7/tcp.7 +++ b/man7/tcp.7 @@ -811,12 +811,18 @@ the urgent pointer: the urgent pointer points to the first byte after the urgent data. Enabling this option may lead to interoperability problems. .TP -.IR tcp_syn_retries " (integer; default: 5; since Linux 2.2)" +.IR tcp_syn_retries " (integer; default: 6; since Linux 2.2)" .\" Since 2.1.38 The maximum number of times initial SYNs for an active TCP connection attempt will be retransmitted. This value should not be higher than 255. -The default value is 5, which corresponds to approximately 180 seconds. +The default value is 6, which corresponds to retrying for up to +approximately 127 seconds. +Before Linux 3.7, +.\" commit 6c9ff979d1921e9fd05d89e1383121c2503759b9 +the default value was 5, which +(in conjunction with calculation based on other kernel parameters) +corresponded to approximately 180 seconds. .TP .IR tcp_synack_retries " (integer; default: 5; since Linux 2.2)" .\" Since 2.1.38