Bug 202885

Summary:	tcp_syn_retries wrong default
Product:	Documentation	Reporter:	vrafaeli
Component:	man-pages	Assignee:	documentation_man-pages (documentation_man-pages)
Status:	RESOLVED CODE_FIX
Severity:	low	CC:	mtk.manpages
Priority:	P1
Hardware:	All
OS:	Linux
Kernel Version:		Subsystem:
Regression:	No	Bisected commit-id:

Description vrafaeli 2019-03-12 08:14:11 UTC

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).

Comment 1 vrafaeli 2019-03-12 08:16:36 UTC

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.

Comment 2 vrafaeli 2019-03-12 10:41:12 UTC

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.

Comment 3 Michael Kerrisk 2020-05-04 10:23:39 UTC

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