.\" This man page is Copyright (C) 1999 Andi Kleen <ak@muc.de>.
+.\" and Copyright (C) 2008 Michael Kerrisk <mtk.manpages@gmail.com>
+.\" Note also that many pieces are drawn from the kernel source file
+.\" Documentation/networking/ip-sysctl.txt.
.\"
.\" %%%LICENSE_START(VERBATIM_ONE_PARA)
.\" Permission is granted to distribute possibly modified copies
.\" (other than the remaining FIXMEs in the page source below).
.\"
.\" FIXME The following need to be documented
-.\" TCP_CONGESTION (new in 2.6.13)
-.\" commit 5f8ef48d240963093451bcf83df89f1a1364f51d
-.\" Author: Stephen Hemminger <shemminger@osdl.org>
.\" TCP_MD5SIG (2.6.20)
.\" commit cfb6eeb4c860592edd123fdea908d23c6ad1c7dc
.\" Author was yoshfuji@linux-ipv6.org
.\" Author: William Allen Simpson <william.allen.simpson@gmail.com>
.\" commit e56fb50f2b7958b931c8a2fc0966061b3f3c8f3a
.\" Author: William Allen Simpson <william.allen.simpson@gmail.com>
+.\"
+.\" REMOVED in Linux 3.10
+.\" commit 1a2c6181c4a1922021b4d7df373bba612c3e5f04
+.\" Author: Christoph Paasch <christoph.paasch@uclouvain.be>
+.\"
.\" TCP_THIN_LINEAR_TIMEOUTS (2.6.34)
.\" commit 36e31b0af58728071e8023cf8e20c5166b700717
.\" Author: Andreas Petlund <apetlund@simula.no>
-.\" TCP_THIN_DUPACK (2..6.34)
+.\" TCP_THIN_DUPACK (2.6.34)
.\" commit 7e38017557bc0b87434d184f8804cadb102bb903
.\" Author: Andreas Petlund <apetlund@simula.no>
-.\" TCP_USER_TIMEOUT (new in 2.6.37)
-.\" Author: Jerry Chu <hkchu@google.com>
-.\" commit dca43c75e7e545694a9dd6288553f55c53e2a3a3
.\" TCP_REPAIR (3.5)
.\" commit ee9952831cfd0bbe834f4a26489d7dce74582e37
.\" Author: Pavel Emelyanov <xemul@parallels.com>
.\" TCP_REPAIR_OPTIONS (3.5)
.\" commit b139ba4e90dccbf4cd4efb112af96a5c9e0b098c
.\" Author: Pavel Emelyanov <xemul@parallels.com>
+.\" TCP_FASTOPEN (3.6)
+.\" (Fast Open server side implementation completed in 3.7)
+.\" http://lwn.net/Articles/508865/
+.\" TCP_TIMESTAMP (3.9)
+.\" commit 93be6ce0e91b6a94783e012b1857a347a5e6e9f2
+.\" Author: Andrey Vagin <avagin@openvz.org>
+.\" TCP_NOTSENT_LOWAT (3.12)
+.\" commit c9bee3b7fdecb0c1d070c7b54113b3bdfb9a3d36
+.\" Author: Eric Dumazet <edumazet@google.com>
.\"
-.TH TCP 7 2013-06-21 "Linux" "Linux Programmer's Manual"
+.TH TCP 7 2014-01-23 "Linux" "Linux Programmer's Manual"
.SH NAME
tcp \- TCP protocol
.SH SYNOPSIS
processes (see the description of the
.B TCP_CONGESTION
socket option).
+The items in the list are separated by white space and
+terminated by a newline character.
The list is a subset of those listed in
.IR tcp_available_congestion_control .
-.\" FIXME How are the items in this delimited? Null bytes, spaces, commas?
The default value for this list is "reno" plus the default setting of
.IR tcp_congestion_control .
.TP
.\" The following is from 2.6.28-rc4: Documentation/networking/ip-sysctl.txt
Show a list of the congestion-control algorithms
that are registered.
-.\" FIXME How are the items in this delimited? Null bytes, spaces, commas?
+The items in the list are separated by white space and
+terminated by a newline character.
This list is a limiting set for the list in
.IR tcp_allowed_congestion_control .
More congestion-control algorithms may be available as modules,
For more information see
.BR ip (7).
.TP
+.BR TCP_CONGESTION " (since Linux 2.6.13)"
+.\" commit 5f8ef48d240963093451bcf83df89f1a1364f51d
+.\" Author: Stephen Hemminger <shemminger@osdl.org>
+The argument for this option is a string.
+This option allows the caller to set the TCP congestion control
+algorithm to be used, on a per-socket basis.
+Unprivileged processes are restricted to choosing one of the algorithms in
+.IR tcp_allowed_congestion_control
+(described above).
+Privileged processes
+.RB ( CAP_NET_ADMIN )
+can choose from any of the available congestion-control algorithms
+(see the description of
+.IR tcp_available_congestion_control
+above).
+.TP
.BR TCP_CORK " (since Linux 2.2)"
.\" precisely: since 2.1.127
If set, don't send out partial frames.
.TP
.BR TCP_DEFER_ACCEPT " (since Linux 2.4)"
.\" Precisely: since 2.3.38
+.\" Useful references:
+.\" http://www.techrepublic.com/article/take-advantage-of-tcp-ip-options-to-optimize-data-transmission/
+.\" http://unix.stackexchange.com/questions/94104/real-world-use-of-tcp-defer-accept
Allow a listener to be awakened only when data arrives on the socket.
Takes an integer value (seconds), this can
bound the maximum number of attempts TCP will make to
It cannot exceed 255.
This option should not be used in code intended to be portable.
.TP
+.BR TCP_USER_TIMEOUT " (since Linux 2.6.37)"
+.\" commit dca43c75e7e545694a9dd6288553f55c53e2a3a3
+.\" Author: Jerry Chu <hkchu@google.com>
+.\" The following text taken nearly verbatim from Jerry Chu's (excellent)
+.\" commit message.
+.\"
+This option takes an
+.IR "unsigned int"
+as an argument.
+When the value is greater than 0,
+it specifies the maximum amount of time in milliseconds that transmitted
+data may remain unacknowledged before TCP will forcibly close the
+corresponding connection and return
+.B ETIMEDOUT
+to the application.
+If the option value is specified as 0,
+TCP will to use the system default.
+
+Increasing user timeouts allows a TCP connection to survive extended
+periods without end-to-end connectivity.
+Decreasing user timeouts
+allows applications to "fail fast", if so desired.
+Otherwise, failure may take up to 20 minutes with
+the current system defaults in a normal WAN environment.
+
+This option can be set during any state of a TCP connection,
+but is only effective during the synchronized states of a connection
+(ESTABLISHED, FIN-WAIT-1, FIN-WAIT-2, CLOSE-WAIT, CLOSING, and LAST-ACK).
+Moreover, when used with the TCP keepalive
+.RB ( SO_KEEPALIVE )
+option,
+.B TCP_USER_TIMEOUT
+will override keepalive to determine when to close a
+connection due to keepalive failure.
+
+The option has no effect on when TCP retransmits a packet,
+nor when a keepalive probe is sent.
+
+This option, like many others, will be inherited by the socket returned by
+.BR accept (2),
+if it was set on the listening socket.
+
+Further details on the user timeout feature can be found in
+RFC\ 793 and RFC\ 5482 ("TCP User Timeout Option").
+.TP
.BR TCP_WINDOW_CLAMP " (since Linux 2.4)"
.\" Precisely: since 2.3.41
Bound the size of the advertised window to this value.
.IR /proc/sys/net/ipv4/tcp_stdurg .
It is possible to peek at out-of-band data using the
-.IR recv (2)
+.BR recv (2)
.B MSG_PEEK
flag.
This flag causes the received bytes of data to be discarded,
rather than passed back in a caller-supplied buffer.
Since Linux 2.4.4,
-.BR MSG_PEEK
+.BR MSG_TRUNC
also has this effect when used in conjunction with
.BR MSG_OOB
to receive out-of-band data.
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