Merging upstream version 6.8.

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 0 insertions, 1563 deletions

diff --git a/man7/tcp.7 b/man7/tcp.7
deleted file mode 100644
index 2b1d333..0000000
--- a/man7/tcp.7
+++ /dev/null
@@ -1,1563 +0,0 @@
-.\" SPDX-License-Identifier: Linux-man-pages-1-para
-.\"
-.\" 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.
-.\"
-.\" 2.4 Updates by Nivedita Singhvi 4/20/02 <nivedita@us.ibm.com>.
-.\" Modified, 2004-11-11, Michael Kerrisk and Andries Brouwer
-.\"	Updated details of interaction of TCP_CORK and TCP_NODELAY.
-.\"
-.\" 2008-11-21, mtk, many, many updates.
-.\"     The descriptions of /proc files and socket options should now
-.\"     be more or less up to date and complete as at Linux 2.6.27
-.\"     (other than the remaining FIXMEs in the page source below).
-.\"
-.\" FIXME The following need to be documented
-.\"	TCP_MD5SIG (2.6.20)
-.\"	    commit cfb6eeb4c860592edd123fdea908d23c6ad1c7dc
-.\"	    Author was yoshfuji@linux-ipv6.org
-.\"	    Needs CONFIG_TCP_MD5SIG
-.\" From net/inet/Kconfig:
-.\" bool "TCP: MD5 Signature Option support (RFC2385) (EXPERIMENTAL)"
-.\" RFC2385 specifies a method of giving MD5 protection to TCP sessions.
-.\" Its main (only?) use is to protect BGP sessions between core routers
-.\" on the Internet.
-.\"
-.\" There is a TCP_MD5SIG option documented in FreeBSD's tcp(4),
-.\" but probably many details are different on Linux
-.\"	    http://thread.gmane.org/gmane.linux.network/47490
-.\"	    http://www.daemon-systems.org/man/tcp.4.html
-.\"	    http://article.gmane.org/gmane.os.netbsd.devel.network/3767/match=tcp_md5sig+freebsd
-.\"
-.\"	TCP_COOKIE_TRANSACTIONS (2.6.33)
-.\"	    commit 519855c508b9a17878c0977a3cdefc09b59b30df
-.\"	    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)
-.\"	    commit 7e38017557bc0b87434d184f8804cadb102bb903
-.\"	    Author: Andreas Petlund <apetlund@simula.no>
-.\"
-.\"	TCP_REPAIR (3.5)
-.\"	    commit ee9952831cfd0bbe834f4a26489d7dce74582e37
-.\"	    Author: Pavel Emelyanov <xemul@parallels.com>
-.\"	    See also
-.\"		http://criu.org/TCP_connection
-.\"		https://lwn.net/Articles/495304/
-.\"
-.\"	TCP_REPAIR_QUEUE (3.5)
-.\"	    commit ee9952831cfd0bbe834f4a26489d7dce74582e37
-.\"	    Author: Pavel Emelyanov <xemul@parallels.com>
-.\"
-.\"	TCP_QUEUE_SEQ (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 Linux 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>
-.\"
-.\"	TCP_CC_INFO (4.1)
-.\"	   commit 6e9250f59ef9efb932c84850cd221f22c2a03c4a
-.\"	   Author: Eric Dumazet <edumazet@google.com>
-.\"
-.\"	TCP_SAVE_SYN, TCP_SAVED_SYN (4.2)
-.\"	    commit cd8ae85299d54155702a56811b2e035e63064d3d
-.\"	    Author: Eric Dumazet <edumazet@google.com>
-.\"
-.TH tcp 7 2023-10-31 "Linux man-pages 6.7"
-.SH NAME
-tcp \- TCP protocol
-.SH SYNOPSIS
-.nf
-.B #include <sys/socket.h>
-.B #include <netinet/in.h>
-.B #include <netinet/tcp.h>
-.P
-.IB tcp_socket " = socket(AF_INET, SOCK_STREAM, 0);"
-.fi
-.SH DESCRIPTION
-This is an implementation of the TCP protocol defined in
-RFC\ 793, RFC\ 1122 and RFC\ 2001 with the NewReno and SACK
-extensions.
-It provides a reliable, stream-oriented,
-full-duplex connection between two sockets on top of
-.BR ip (7),
-for both v4 and v6 versions.
-TCP guarantees that the data arrives in order and
-retransmits lost packets.
-It generates and checks a per-packet checksum to catch
-transmission errors.
-TCP does not preserve record boundaries.
-.P
-A newly created TCP socket has no remote or local address and is not
-fully specified.
-To create an outgoing TCP connection use
-.BR connect (2)
-to establish a connection to another TCP socket.
-To receive new incoming connections, first
-.BR bind (2)
-the socket to a local address and port and then call
-.BR listen (2)
-to put the socket into the listening state.
-After that a new socket for each incoming connection can be accepted using
-.BR accept (2).
-A socket which has had
-.BR accept (2)
-or
-.BR connect (2)
-successfully called on it is fully specified and may transmit data.
-Data cannot be transmitted on listening or not yet connected sockets.
-.P
-Linux supports RFC\ 1323 TCP high performance
-extensions.
-These include Protection Against Wrapped
-Sequence Numbers (PAWS), Window Scaling and Timestamps.
-Window scaling allows the use
-of large (> 64\ kB) TCP windows in order to support links with high
-latency or bandwidth.
-To make use of them, the send and receive buffer sizes must be increased.
-They can be set globally with the
-.I /proc/sys/net/ipv4/tcp_wmem
-and
-.I /proc/sys/net/ipv4/tcp_rmem
-files, or on individual sockets by using the
-.B SO_SNDBUF
-and
-.B SO_RCVBUF
-socket options with the
-.BR setsockopt (2)
-call.
-.P
-The maximum sizes for socket buffers declared via the
-.B SO_SNDBUF
-and
-.B SO_RCVBUF
-mechanisms are limited by the values in the
-.I /proc/sys/net/core/rmem_max
-and
-.I /proc/sys/net/core/wmem_max
-files.
-Note that TCP actually allocates twice the size of
-the buffer requested in the
-.BR setsockopt (2)
-call, and so a succeeding
-.BR getsockopt (2)
-call will not return the same size of buffer as requested in the
-.BR setsockopt (2)
-call.
-TCP uses the extra space for administrative purposes and internal
-kernel structures, and the
-.I /proc
-file values reflect the
-larger sizes compared to the actual TCP windows.
-On individual connections, the socket buffer size must be set prior to the
-.BR listen (2)
-or
-.BR connect (2)
-calls in order to have it take effect.
-See
-.BR socket (7)
-for more information.
-.P
-TCP supports urgent data.
-Urgent data is used to signal the
-receiver that some important message is part of the data
-stream and that it should be processed as soon as possible.
-To send urgent data specify the
-.B MSG_OOB
-option to
-.BR send (2).
-When urgent data is received, the kernel sends a
-.B SIGURG
-signal to the process or process group that has been set as the
-socket "owner" using the
-.B SIOCSPGRP
-or
-.B FIOSETOWN
-ioctls (or the POSIX.1-specified
-.BR fcntl (2)
-.B F_SETOWN
-operation).
-When the
-.B SO_OOBINLINE
-socket option is enabled, urgent data is put into the normal
-data stream (a program can test for its location using the
-.B SIOCATMARK
-ioctl described below),
-otherwise it can be received only when the
-.B MSG_OOB
-flag is set for
-.BR recv (2)
-or
-.BR recvmsg (2).
-.P
-When out-of-band data is present,
-.BR select (2)
-indicates the file descriptor as having an exceptional condition and
-.I poll (2)
-indicates a
-.B POLLPRI
-event.
-.P
-Linux 2.4 introduced a number of changes for improved
-throughput and scaling, as well as enhanced functionality.
-Some of these features include support for zero-copy
-.BR sendfile (2),
-Explicit Congestion Notification, new
-management of TIME_WAIT sockets, keep-alive socket options
-and support for Duplicate SACK extensions.
-.SS Address formats
-TCP is built on top of IP (see
-.BR ip (7)).
-The address formats defined by
-.BR ip (7)
-apply to TCP.
-TCP supports point-to-point communication only;
-broadcasting and multicasting are not
-supported.
-.SS /proc interfaces
-System-wide TCP parameter settings can be accessed by files in the directory
-.IR /proc/sys/net/ipv4/ .
-In addition, most IP
-.I /proc
-interfaces also apply to TCP; see
-.BR ip (7).
-Variables described as
-.I Boolean
-take an integer value, with a nonzero value ("true") meaning that
-the corresponding option is enabled, and a zero value ("false")
-meaning that the option is disabled.
-.TP
-.IR tcp_abc " (Integer; default: 0; Linux 2.6.15 to Linux 3.8)"
-.\" Since Linux 2.6.15; removed in Linux 3.9
-.\" commit ca2eb5679f8ddffff60156af42595df44a315ef0
-.\" The following is from Linux 2.6.28-rc4: Documentation/networking/ip-sysctl.txt
-Control the Appropriate Byte Count (ABC), defined in RFC 3465.
-ABC is a way of increasing the congestion window
-.RI ( cwnd )
-more slowly in response to partial acknowledgements.
-Possible values are:
-.RS
-.TP
-.B 0
-increase
-.I cwnd
-once per acknowledgement (no ABC)
-.TP
-.B 1
-increase
-.I cwnd
-once per acknowledgement of full sized segment
-.TP
-.B 2
-allow increase
-.I cwnd
-by two if acknowledgement is
-of two segments to compensate for delayed acknowledgements.
-.RE
-.TP
-.IR tcp_abort_on_overflow " (Boolean; default: disabled; since Linux 2.4)"
-.\" Since Linux 2.3.41
-Enable resetting connections if the listening service is too
-slow and unable to keep up and accept them.
-It means that if overflow occurred due
-to a burst, the connection will recover.
-Enable this option
-.I only
-if you are really sure that the listening daemon
-cannot be tuned to accept connections faster.
-Enabling this option can harm the clients of your server.
-.TP
-.IR tcp_adv_win_scale " (integer; default: 2; since Linux 2.4)"
-.\" Since Linux 2.4.0-test7
-Count buffering overhead as
-.IR "bytes/2\[ha]tcp_adv_win_scale" ,
-if
-.I tcp_adv_win_scale
-is greater than 0; or
-.IR "bytes\-bytes/2\[ha](\-tcp_adv_win_scale)" ,
-if
-.I tcp_adv_win_scale
-is less than or equal to zero.
-.IP
-The socket receive buffer space is shared between the
-application and kernel.
-TCP maintains part of the buffer as
-the TCP window, this is the size of the receive window
-advertised to the other end.
-The rest of the space is used
-as the "application" buffer, used to isolate the network
-from scheduling and application latencies.
-The
-.I tcp_adv_win_scale
-default value of 2 implies that the space
-used for the application buffer is one fourth that of the total.
-.TP
-.IR tcp_allowed_congestion_control " (String; default: see text; since Linux 2.4.20)"
-.\" The following is from Linux 2.6.28-rc4: Documentation/networking/ip-sysctl.txt
-Show/set the congestion control algorithm choices available to unprivileged
-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 .
-The default value for this list is "reno" plus the default setting of
-.IR tcp_congestion_control .
-.TP
-.IR tcp_autocorking " (Boolean; default: enabled; since Linux 3.14)"
-.\" commit f54b311142a92ea2e42598e347b84e1655caf8e3
-.\" Text heavily based on Documentation/networking/ip-sysctl.txt
-If this option is enabled, the kernel tries to coalesce small writes
-(from consecutive
-.BR write (2)
-and
-.BR sendmsg (2)
-calls) as much as possible,
-in order to decrease the total number of sent packets.
-Coalescing is done if at least one prior packet for the flow
-is waiting in Qdisc queues or device transmit queue.
-Applications can still use the
-.B TCP_CORK
-socket option to obtain optimal behavior
-when they know how/when to uncork their sockets.
-.TP
-.IR tcp_available_congestion_control " (String; read-only; since Linux 2.4.20)"
-.\" The following is from Linux 2.6.28-rc4: Documentation/networking/ip-sysctl.txt
-Show a list of the congestion-control algorithms
-that are registered.
-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,
-but not loaded.
-.TP
-.IR tcp_app_win  " (integer; default: 31; since Linux 2.4)"
-.\" Since Linux 2.4.0-test7
-This variable defines how many
-bytes of the TCP window are reserved for buffering overhead.
-.IP
-A maximum of (\fIwindow/2\[ha]tcp_app_win\fP, mss) bytes in the window
-are reserved for the application buffer.
-A value of 0 implies that no amount is reserved.
-.\"
-.\" The following is from Linux 2.6.28-rc4: Documentation/networking/ip-sysctl.txt
-.TP
-.IR tcp_base_mss " (Integer; default: 512; since Linux 2.6.17)"
-The initial value of
-.I search_low
-to be used by the packetization layer Path MTU discovery (MTU probing).
-If MTU probing is enabled,
-this is the initial MSS used by the connection.
-.\"
-.\" The following is from Linux 2.6.12: Documentation/networking/ip-sysctl.txt
-.TP
-.IR tcp_bic " (Boolean; default: disabled; Linux 2.4.27/2.6.6 to Linux 2.6.13)"
-Enable BIC TCP congestion control algorithm.
-BIC-TCP is a sender-side-only change that ensures a linear RTT
-fairness under large windows while offering both scalability and
-bounded TCP-friendliness.
-The protocol combines two schemes
-called additive increase and binary search increase.
-When the congestion window is large, additive increase with a large
-increment ensures linear RTT fairness as well as good scalability.
-Under small congestion windows, binary search
-increase provides TCP friendliness.
-.\"
-.\" The following is from Linux 2.6.12: Documentation/networking/ip-sysctl.txt
-.TP
-.IR tcp_bic_low_window " (integer; default: 14; Linux 2.4.27/2.6.6 to Linux 2.6.13)"
-Set the threshold window (in packets) where BIC TCP starts to
-adjust the congestion window.
-Below this threshold BIC TCP behaves the same as the default TCP Reno.
-.\"
-.\" The following is from Linux 2.6.12: Documentation/networking/ip-sysctl.txt
-.TP
-.IR tcp_bic_fast_convergence " (Boolean; default: enabled; Linux 2.4.27/2.6.6 to Linux 2.6.13)"
-Force BIC TCP to more quickly respond to changes in congestion window.
-Allows two flows sharing the same connection to converge more rapidly.
-.TP
-.IR tcp_congestion_control " (String; default: see text; since Linux 2.4.13)"
-.\" The following is from Linux 2.6.28-rc4: Documentation/networking/ip-sysctl.txt
-Set the default congestion-control algorithm to be used for new connections.
-The algorithm "reno" is always available,
-but additional choices may be available depending on kernel configuration.
-The default value for this file is set as part of kernel configuration.
-.TP
-.IR tcp_dma_copybreak " (integer; default: 4096; since Linux 2.6.24)"
-Lower limit, in bytes, of the size of socket reads that will be
-offloaded to a DMA copy engine, if one is present in the system
-and the kernel was configured with the
-.B CONFIG_NET_DMA
-option.
-.TP
-.IR tcp_dsack " (Boolean; default: enabled; since Linux 2.4)"
-.\" Since Linux 2.4.0-test7
-Enable RFC\ 2883 TCP Duplicate SACK support.
-.TP
-.IR tcp_fastopen " (Bitmask; default: 0x1; since Linux 3.7)"
-Enables RFC\~7413 Fast Open support.
-The flag is used as a bitmap with the following values:
-.RS
-.TP
-.B 0x1
-Enables client side Fast Open support
-.TP
-.B 0x2
-Enables server side Fast Open support
-.TP
-.B 0x4
-Allows client side to transmit data in SYN without Fast Open option
-.TP
-.B 0x200
-Allows server side to accept SYN data without Fast Open option
-.TP
-.B 0x400
-Enables Fast Open on all listeners without
-.B TCP_FASTOPEN
-socket option
-.RE
-.TP
-.IR tcp_fastopen_key " (since Linux 3.7)"
-Set server side RFC\~7413 Fast Open key to generate Fast Open cookie
-when server side Fast Open support is enabled.
-.TP
-.IR tcp_ecn " (Integer; default: see below; since Linux 2.4)"
-.\" Since Linux 2.4.0-test7
-Enable RFC\ 3168 Explicit Congestion Notification.
-.IP
-This file can have one of the following values:
-.RS
-.TP
-.B 0
-Disable ECN.
-Neither initiate nor accept ECN.
-This was the default up to and including Linux 2.6.30.
-.TP
-.B 1
-Enable ECN when requested by incoming connections and also
-request ECN on outgoing connection attempts.
-.TP
-.B 2
-.\" commit 255cac91c3c9ce7dca7713b93ab03c75b7902e0e
-Enable ECN when requested by incoming connections,
-but do not request ECN on outgoing connections.
-This value is supported, and is the default, since Linux 2.6.31.
-.RE
-.IP
-When enabled, connectivity to some destinations could be affected
-due to older, misbehaving middle boxes along the path, causing
-connections to be dropped.
-However, to facilitate and encourage deployment with option 1, and
-to work around such buggy equipment, the
-.B tcp_ecn_fallback
-option has been introduced.
-.TP
-.IR tcp_ecn_fallback " (Boolean; default: enabled; since Linux 4.1)"
-.\" commit 492135557dc090a1abb2cfbe1a412757e3ed68ab
-Enable RFC\ 3168, Section 6.1.1.1. fallback.
-When enabled, outgoing ECN-setup SYNs that time out within the
-normal SYN retransmission timeout will be resent with CWR and
-ECE cleared.
-.TP
-.IR tcp_fack " (Boolean; default: enabled; since Linux 2.2)"
-.\" Since Linux 2.1.92
-Enable TCP Forward Acknowledgement support.
-.TP
-.IR tcp_fin_timeout " (integer; default: 60; since Linux 2.2)"
-.\" Since Linux 2.1.53
-This specifies how many seconds to wait for a final FIN packet before the
-socket is forcibly closed.
-This is strictly a violation of the TCP specification,
-but required to prevent denial-of-service attacks.
-In Linux 2.2, the default value was 180.
-.\"
-.\" The following is from Linux 2.6.12: Documentation/networking/ip-sysctl.txt
-.TP
-.IR tcp_frto " (integer; default: see below; since Linux 2.4.21/2.6)"
-.\" Since Linux 2.4.21/2.5.43
-Enable F-RTO, an enhanced recovery algorithm for TCP retransmission
-timeouts (RTOs).
-It is particularly beneficial in wireless environments
-where packet loss is typically due to random radio interference
-rather than intermediate router congestion.
-See RFC 4138 for more details.
-.IP
-This file can have one of the following values:
-.RS
-.TP
-.B 0
-Disabled.
-This was the default up to and including Linux 2.6.23.
-.TP
-.B 1
-The basic version F-RTO algorithm is enabled.
-.TP
-.B 2
-.\" commit c96fd3d461fa495400df24be3b3b66f0e0b152f9
-Enable SACK-enhanced F-RTO if flow uses SACK.
-The basic version can be used also when
-SACK is in use though in that case scenario(s) exists where F-RTO
-interacts badly with the packet counting of the SACK-enabled TCP flow.
-This value is the default since Linux 2.6.24.
-.RE
-.IP
-Before Linux 2.6.22, this parameter was a Boolean value,
-supporting just values 0 and 1 above.
-.TP
-.IR tcp_frto_response " (integer; default: 0; since Linux 2.6.22)"
-When F-RTO has detected that a TCP retransmission timeout was spurious
-(i.e., the timeout would have been avoided had TCP set a
-longer retransmission timeout),
-TCP has several options concerning what to do next.
-Possible values are:
-.RS
-.TP
-.B 0
-Rate halving based; a smooth and conservative response,
-results in halved congestion window
-.RI ( cwnd )
-and slow-start threshold
-.RI ( ssthresh )
-after one RTT.
-.TP
-.B 1
-Very conservative response; not recommended because even
-though being valid, it interacts poorly with the rest of Linux TCP; halves
-.I cwnd
-and
-.I ssthresh
-immediately.
-.TP
-.B 2
-Aggressive response; undoes congestion-control measures
-that are now known to be unnecessary
-(ignoring the possibility of a lost retransmission that would require
-TCP to be more cautious);
-.I cwnd
-and
-.I ssthresh
-are restored to the values prior to timeout.
-.RE
-.TP
-.IR tcp_keepalive_intvl " (integer; default: 75; since Linux 2.4)"
-.\" Since Linux 2.3.18
-The number of seconds between TCP keep-alive probes.
-.TP
-.IR tcp_keepalive_probes " (integer; default: 9; since Linux 2.2)"
-.\" Since Linux 2.1.43
-The maximum number of TCP keep-alive probes to send
-before giving up and killing the connection if
-no response is obtained from the other end.
-.TP
-.IR tcp_keepalive_time " (integer; default: 7200; since Linux 2.2)"
-.\" Since Linux 2.1.43
-The number of seconds a connection needs to be idle
-before TCP begins sending out keep-alive probes.
-Keep-alives are sent only when the
-.B SO_KEEPALIVE
-socket option is enabled.
-The default value is 7200 seconds (2 hours).
-An idle connection is terminated after
-approximately an additional 11 minutes (9 probes an interval
-of 75 seconds apart) when keep-alive is enabled.
-.IP
-Note that underlying connection tracking mechanisms and
-application timeouts may be much shorter.
-.\"
-.\" The following is from Linux 2.6.12: Documentation/networking/ip-sysctl.txt
-.TP
-.IR tcp_low_latency  " (Boolean; default: disabled; since Linux 2.4.21/2.6; \
-obsolete since Linux 4.14)"
-.\" Since Linux 2.4.21/2.5.60
-If enabled, the TCP stack makes decisions that prefer lower
-latency as opposed to higher throughput.
-It this option is disabled, then higher throughput is preferred.
-An example of an application where this default should be
-changed would be a Beowulf compute cluster.
-Since Linux 4.14,
-.\" commit b6690b14386698ce2c19309abad3f17656bdfaea
-this file still exists, but its value is ignored.
-.TP
-.IR tcp_max_orphans  " (integer; default: see below; since Linux 2.4)"
-.\" Since Linux 2.3.41
-The maximum number of orphaned (not attached to any user file
-handle) TCP sockets allowed in the system.
-When this number is exceeded,
-the orphaned connection is reset and a warning is printed.
-This limit exists only to prevent simple denial-of-service attacks.
-Lowering this limit is not recommended.
-Network conditions might require you to increase the number of
-orphans allowed, but note that each orphan can eat up to \[ti]64\ kB
-of unswappable memory.
-The default initial value is set equal to the kernel parameter NR_FILE.
-This initial default is adjusted depending on the memory in the system.
-.TP
-.IR tcp_max_syn_backlog " (integer; default: see below; since Linux 2.2)"
-.\" Since Linux 2.1.53
-The maximum number of queued connection requests which have
-still not received an acknowledgement from the connecting client.
-If this number is exceeded, the kernel will begin
-dropping requests.
-The default value of 256 is increased to
-1024 when the memory present in the system is adequate or
-greater (>= 128\ MB), and reduced to 128 for those systems with
-very low memory (<= 32\ MB).
-.IP
-Before Linux 2.6.20,
-.\" commit 72a3effaf633bcae9034b7e176bdbd78d64a71db
-it was recommended that if this needed to be increased above 1024,
-the size of the SYNACK hash table
-.RB ( TCP_SYNQ_HSIZE )
-in
-.I include/net/tcp.h
-should be modified to keep
-.IP
-.in +4n
-.EX
-TCP_SYNQ_HSIZE * 16 <= tcp_max_syn_backlog
-.EE
-.in
-.IP
-and the kernel should be
-recompiled.
-In Linux 2.6.20, the fixed sized
-.B TCP_SYNQ_HSIZE
-was removed in favor of dynamic sizing.
-.TP
-.IR tcp_max_tw_buckets " (integer; default: see below; since Linux 2.4)"
-.\" Since Linux 2.3.41
-The maximum number of sockets in TIME_WAIT state allowed in
-the system.
-This limit exists only to prevent simple denial-of-service attacks.
-The default value of NR_FILE*2 is adjusted
-depending on the memory in the system.
-If this number is
-exceeded, the socket is closed and a warning is printed.
-.TP
-.IR tcp_moderate_rcvbuf " (Boolean; default: enabled; since Linux 2.4.17/2.6.7)"
-.\" The following is from Linux 2.6.28-rc4: Documentation/networking/ip-sysctl.txt
-If enabled, TCP performs receive buffer auto-tuning,
-attempting to automatically size the buffer (no greater than
-.IR tcp_rmem[2] )
-to match the size required by the path for full throughput.
-.TP
-.IR tcp_mem " (since Linux 2.4)"
-.\" Since Linux 2.4.0-test7
-This is a vector of 3 integers: [low, pressure, high].
-These bounds, measured in units of the system page size,
-are used by TCP to track its memory usage.
-The defaults are calculated at boot time from the amount of
-available memory.
-(TCP can only use
-.I "low memory"
-for this, which is limited to around 900 megabytes on 32-bit systems.
-64-bit systems do not suffer this limitation.)
-.RS
-.TP
-.I low
-TCP doesn't regulate its memory allocation when the number
-of pages it has allocated globally is below this number.
-.TP
-.I pressure
-When the amount of memory allocated by TCP
-exceeds this number of pages, TCP moderates its memory consumption.
-This memory pressure state is exited
-once the number of pages allocated falls below
-the
-.I low
-mark.
-.TP
-.I high
-The maximum number of pages, globally, that TCP will allocate.
-This value overrides any other limits imposed by the kernel.
-.RE
-.TP
-.IR tcp_mtu_probing " (integer; default: 0; since Linux 2.6.17)"
-.\" The following is from Linux 2.6.28-rc4: Documentation/networking/ip-sysctl.txt
-This parameter controls TCP Packetization-Layer Path MTU Discovery.
-The following values may be assigned to the file:
-.RS
-.TP
-.B 0
-Disabled
-.TP
-.B 1
-Disabled by default, enabled when an ICMP black hole detected
-.TP
-.B 2
-Always enabled, use initial MSS of
-.IR tcp_base_mss .
-.RE
-.TP
-.IR tcp_no_metrics_save " (Boolean; default: disabled; since Linux 2.6.6)"
-.\" The following is from Linux 2.6.28-rc4: Documentation/networking/ip-sysctl.txt
-By default, TCP saves various connection metrics in the route cache
-when the connection closes, so that connections established in the
-near future can use these to set initial conditions.
-Usually, this increases overall performance,
-but it may sometimes cause performance degradation.
-If
-.I tcp_no_metrics_save
-is enabled, TCP will not cache metrics on closing connections.
-.TP
-.IR tcp_orphan_retries " (integer; default: 8; since Linux 2.4)"
-.\" Since Linux 2.3.41
-The maximum number of attempts made to probe the other
-end of a connection which has been closed by our end.
-.TP
-.IR tcp_reordering " (integer; default: 3; since Linux 2.4)"
-.\" Since Linux 2.4.0-test7
-The maximum a packet can be reordered in a TCP packet stream
-without TCP assuming packet loss and going into slow start.
-It is not advisable to change this number.
-This is a packet reordering detection metric designed to
-minimize unnecessary back off and retransmits provoked by
-reordering of packets on a connection.
-.TP
-.IR tcp_retrans_collapse " (Boolean; default: enabled; since Linux 2.2)"
-.\" Since Linux 2.1.96
-Try to send full-sized packets during retransmit.
-.TP
-.IR tcp_retries1 " (integer; default: 3; since Linux 2.2)"
-.\" Since Linux 2.1.43
-The number of times TCP will attempt to retransmit a
-packet on an established connection normally,
-without the extra effort of getting the network layers involved.
-Once we exceed this number of
-retransmits, we first have the network layer
-update the route if possible before each new retransmit.
-The default is the RFC specified minimum of 3.
-.TP
-.IR tcp_retries2 " (integer; default: 15; since Linux 2.2)"
-.\" Since Linux 2.1.43
-The maximum number of times a TCP packet is retransmitted
-in established state before giving up.
-The default value is 15, which corresponds to a duration of
-approximately between 13 to 30 minutes, depending
-on the retransmission timeout.
-The RFC\ 1122 specified
-minimum limit of 100 seconds is typically deemed too short.
-.TP
-.IR tcp_rfc1337 " (Boolean; default: disabled; since Linux 2.2)"
-.\" Since Linux 2.1.90
-Enable TCP behavior conformant with RFC\ 1337.
-When disabled,
-if a RST is received in TIME_WAIT state, we close
-the socket immediately without waiting for the end
-of the TIME_WAIT period.
-.TP
-.IR tcp_rmem " (since Linux 2.4)"
-.\" Since Linux 2.4.0-test7
-This is a vector of 3 integers: [min, default, max].
-These parameters are used by TCP to regulate receive buffer sizes.
-TCP dynamically adjusts the size of the
-receive buffer from the defaults listed below, in the range
-of these values, depending on memory available in the system.
-.RS
-.TP
-.I min
-minimum size of the receive buffer used by each TCP socket.
-The default value is the system page size.
-(On Linux 2.4, the default value is 4\ kB, lowered to
-.B PAGE_SIZE
-bytes in low-memory systems.)
-This value
-is used to ensure that in memory pressure mode,
-allocations below this size will still succeed.
-This is not
-used to bound the size of the receive buffer declared
-using
-.B SO_RCVBUF
-on a socket.
-.TP
-.I default
-the default size of the receive buffer for a TCP socket.
-This value overwrites the initial default buffer size from
-the generic global
-.I net.core.rmem_default
-defined for all protocols.
-The default value is 87380 bytes.
-(On Linux 2.4, this will be lowered to 43689 in low-memory systems.)
-If larger receive buffer sizes are desired, this value should
-be increased (to affect all sockets).
-To employ large TCP windows, the
-.I net.ipv4.tcp_window_scaling
-must be enabled (default).
-.TP
-.I max
-the maximum size of the receive buffer used by each TCP socket.
-This value does not override the global
-.IR net.core.rmem_max .
-This is not used to limit the size of the receive buffer declared using
-.B SO_RCVBUF
-on a socket.
-The default value is calculated using the formula
-.IP
-.in +4n
-.EX
-max(87380, min(4\ MB, \fItcp_mem\fP[1]*PAGE_SIZE/128))
-.EE
-.in
-.IP
-(On Linux 2.4, the default is 87380*2 bytes,
-lowered to 87380 in low-memory systems).
-.RE
-.TP
-.IR tcp_sack " (Boolean; default: enabled; since Linux 2.2)"
-.\" Since Linux 2.1.36
-Enable RFC\ 2018 TCP Selective Acknowledgements.
-.TP
-.IR tcp_slow_start_after_idle " (Boolean; default: enabled; since Linux 2.6.18)"
-.\" The following is from Linux 2.6.28-rc4: Documentation/networking/ip-sysctl.txt
-If enabled, provide RFC 2861 behavior and time out the congestion
-window after an idle period.
-An idle period is defined as the current RTO (retransmission timeout).
-If disabled, the congestion window will not
-be timed out after an idle period.
-.TP
-.IR tcp_stdurg " (Boolean; default: disabled; since Linux 2.2)"
-.\" Since Linux 2.1.44
-If this option is enabled, then use the RFC\ 1122 interpretation
-of the TCP urgent-pointer field.
-.\" RFC 793 was ambiguous in its specification of the meaning of the
-.\" urgent pointer.  RFC 1122 (and RFC 961) fixed on a particular
-.\" resolution of this ambiguity (unfortunately the "wrong" one).
-According to this interpretation, the urgent pointer points
-to the last byte of urgent data.
-If this option is disabled, then use the BSD-compatible interpretation of
-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: 6; since Linux 2.2)"
-.\" Since Linux 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 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 Linux 2.1.38
-The maximum number of times a SYN/ACK segment
-for a passive TCP connection will be retransmitted.
-This number should not be higher than 255.
-.TP
-.IR tcp_syncookies " (integer; default: 1; since Linux 2.2)"
-.\" Since Linux 2.1.43
-Enable TCP syncookies.
-The kernel must be compiled with
-.BR CONFIG_SYN_COOKIES .
-The syncookies feature attempts to protect a
-socket from a SYN flood attack.
-This should be used as a last resort, if at all.
-This is a violation of the TCP protocol,
-and conflicts with other areas of TCP such as TCP extensions.
-It can cause problems for clients and relays.
-It is not recommended as a tuning mechanism for heavily
-loaded servers to help with overloaded or misconfigured conditions.
-For recommended alternatives see
-.IR tcp_max_syn_backlog ,
-.IR tcp_synack_retries ,
-and
-.IR tcp_abort_on_overflow .
-Set to one of the following values:
-.RS
-.TP
-.B 0
-Disable TCP syncookies.
-.TP
-.B 1
-Send out syncookies when the syn backlog queue of a socket overflows.
-.TP
-.B 2
-(since Linux 3.12)
-.\" commit 5ad37d5deee1ff7150a2d0602370101de158ad86
-Send out syncookies unconditionally.
-This can be useful for network testing.
-.RE
-.TP
-.IR tcp_timestamps " (integer; default: 1; since Linux 2.2)"
-.\" Since Linux 2.1.36
-Set to one of the following values to enable or disable RFC\ 1323
-TCP timestamps:
-.RS
-.TP
-.B 0
-Disable timestamps.
-.TP
-.B 1
-Enable timestamps as defined in RFC1323 and use random offset for
-each connection rather than only using the current time.
-.TP
-.B 2
-As for the value 1, but without random offsets.
-.\" commit 25429d7b7dca01dc4f17205de023a30ca09390d0
-Setting
-.I tcp_timestamps
-to this value is meaningful since Linux 4.10.
-.RE
-.TP
-.IR tcp_tso_win_divisor " (integer; default: 3; since Linux 2.6.9)"
-This parameter controls what percentage of the congestion window
-can be consumed by a single TCP Segmentation Offload (TSO) frame.
-The setting of this parameter is a tradeoff between burstiness and
-building larger TSO frames.
-.TP
-.IR tcp_tw_recycle " (Boolean; default: disabled; Linux 2.4 to Linux 4.11)"
-.\" Since Linux 2.3.15
-.\" removed in Linux 4.12; commit 4396e46187ca5070219b81773c4e65088dac50cc
-Enable fast recycling of TIME_WAIT sockets.
-Enabling this option is
-not recommended as the remote IP may not use monotonically increasing
-timestamps (devices behind NAT, devices with per-connection timestamp
-offsets).
-See RFC 1323 (PAWS) and RFC 6191.
-.\"
-.\" The following is from Linux 2.6.12: Documentation/networking/ip-sysctl.txt
-.TP
-.IR tcp_tw_reuse " (Boolean; default: disabled; since Linux 2.4.19/2.6)"
-.\" Since Linux 2.4.19/2.5.43
-Allow to reuse TIME_WAIT sockets for new connections when it is
-safe from protocol viewpoint.
-It should not be changed without advice/request of technical experts.
-.\"
-.\" The following is from Linux 2.6.12: Documentation/networking/ip-sysctl.txt
-.TP
-.IR tcp_vegas_cong_avoid  " (Boolean; default: disabled; Linux 2.2 to Linux 2.6.13)"
-.\" Since Linux 2.1.8; removed in Linux 2.6.13
-Enable TCP Vegas congestion avoidance algorithm.
-TCP Vegas is a sender-side-only change to TCP that anticipates
-the onset of congestion by estimating the bandwidth.
-TCP Vegas adjusts the sending rate by modifying the congestion window.
-TCP Vegas should provide less packet loss, but it is
-not as aggressive as TCP Reno.
-.\"
-.\" The following is from Linux 2.6.12: Documentation/networking/ip-sysctl.txt
-.TP
-.IR tcp_westwood " (Boolean; default: disabled; Linux 2.4.26/2.6.3 to Linux 2.6.13)"
-Enable TCP Westwood+ congestion control algorithm.
-TCP Westwood+ is a sender-side-only modification of the TCP Reno
-protocol stack that optimizes the performance of TCP congestion control.
-It is based on end-to-end bandwidth estimation to set
-congestion window and slow start threshold after a congestion episode.
-Using this estimation, TCP Westwood+ adaptively sets a
-slow start threshold and a congestion window which takes into
-account the bandwidth used at the time congestion is experienced.
-TCP Westwood+ significantly increases fairness with respect to
-TCP Reno in wired networks and throughput over wireless links.
-.TP
-.IR tcp_window_scaling " (Boolean; default: enabled; since Linux 2.2)"
-.\" Since Linux 2.1.36
-Enable RFC\ 1323 TCP window scaling.
-This feature allows the use of a large window
-(> 64\ kB) on a TCP connection, should the other end support it.
-Normally, the 16 bit window length field in the TCP header
-limits the window size to less than 64\ kB.
-If larger windows are desired, applications can increase the size of
-their socket buffers and the window scaling option will be employed.
-If
-.I tcp_window_scaling
-is disabled, TCP will not negotiate the use of window
-scaling with the other end during connection setup.
-.TP
-.IR tcp_wmem " (since Linux 2.4)"
-.\" Since Linux 2.4.0-test7
-This is a vector of 3 integers: [min, default, max].
-These parameters are used by TCP to regulate send buffer sizes.
-TCP dynamically adjusts the size of the send buffer from the
-default values listed below, in the range of these values,
-depending on memory available.
-.RS
-.TP
-.I min
-Minimum size of the send buffer used by each TCP socket.
-The default value is the system page size.
-(On Linux 2.4, the default value is 4\ kB.)
-This value is used to ensure that in memory pressure mode,
-allocations below this size will still succeed.
-This is not used to bound the size of the send buffer declared using
-.B SO_SNDBUF
-on a socket.
-.TP
-.I default
-The default size of the send buffer for a TCP socket.
-This value overwrites the initial default buffer size from
-the generic global
-.I /proc/sys/net/core/wmem_default
-defined for all protocols.
-The default value is 16\ kB.
-.\" True in Linux 2.4 and 2.6
-If larger send buffer sizes are desired, this value
-should be increased (to affect all sockets).
-To employ large TCP windows, the
-.I /proc/sys/net/ipv4/tcp_window_scaling
-must be set to a nonzero value (default).
-.TP
-.I max
-The maximum size of the send buffer used by each TCP socket.
-This value does not override the value in
-.IR /proc/sys/net/core/wmem_max .
-This is not used to limit the size of the send buffer declared using
-.B SO_SNDBUF
-on a socket.
-The default value is calculated using the formula
-.IP
-.in +4n
-.EX
-max(65536, min(4\ MB, \fItcp_mem\fP[1]*PAGE_SIZE/128))
-.EE
-.in
-.IP
-(On Linux 2.4, the default value is 128\ kB,
-lowered 64\ kB depending on low-memory systems.)
-.RE
-.TP
-.IR tcp_workaround_signed_windows " (Boolean; default: disabled; since Linux 2.6.26)"
-If enabled, assume that no receipt of a window-scaling option means that the
-remote TCP is broken and treats the window as a signed quantity.
-If disabled, assume that the remote TCP is not broken even if we do
-not receive a window scaling option from it.
-.SS Socket options
-To set or get a TCP socket option, call
-.BR getsockopt (2)
-to read or
-.BR setsockopt (2)
-to write the option with the option level argument set to
-.BR IPPROTO_TCP .
-Unless otherwise noted,
-.I optval
-is a pointer to an
-.IR int .
-.\" or SOL_TCP on Linux
-In addition,
-most
-.B IPPROTO_IP
-socket options are valid on TCP sockets.
-For more information see
-.BR ip (7).
-.P
-Following is a list of TCP-specific socket options.
-For details of some other socket options that are also applicable
-for TCP sockets, see
-.BR socket (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
-.I 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
-.I tcp_available_congestion_control
-above).
-.TP
-.BR TCP_CORK " (since Linux 2.2)"
-.\" precisely: since Linux 2.1.127
-If set, don't send out partial frames.
-All queued partial frames are sent when the option is cleared again.
-This is useful for prepending headers before calling
-.BR sendfile (2),
-or for throughput optimization.
-As currently implemented, there is a 200 millisecond ceiling on the time
-for which output is corked by
-.BR TCP_CORK .
-If this ceiling is reached, then queued data is automatically transmitted.
-This option can be combined with
-.B TCP_NODELAY
-only since Linux 2.5.71.
-This option should not be used in code intended to be portable.
-.TP
-.BR TCP_DEFER_ACCEPT " (since Linux 2.4)"
-.\" Precisely: since Linux 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
-complete the connection.
-This option should not be used in code intended to be portable.
-.TP
-.BR TCP_INFO " (since Linux 2.4)"
-Used to collect information about this socket.
-The kernel returns a \fIstruct tcp_info\fP as defined in the file
-.IR /usr/include/linux/tcp.h .
-This option should not be used in code intended to be portable.
-.TP
-.BR TCP_KEEPCNT " (since Linux 2.4)"
-.\" Precisely: since Linux 2.3.18
-The maximum number of keepalive probes TCP should send
-before dropping the connection.
-This option should not be
-used in code intended to be portable.
-.TP
-.BR TCP_KEEPIDLE " (since Linux 2.4)"
-.\" Precisely: since Linux 2.3.18
-The time (in seconds) the connection needs to remain idle
-before TCP starts sending keepalive probes, if the socket
-option
-.B SO_KEEPALIVE
-has been set on this socket.
-This option should not be used in code intended to be portable.
-.TP
-.BR TCP_KEEPINTVL " (since Linux 2.4)"
-.\" Precisely: since Linux 2.3.18
-The time (in seconds) between individual keepalive probes.
-This option should not be used in code intended to be portable.
-.TP
-.BR TCP_LINGER2 " (since Linux 2.4)"
-.\" Precisely: since Linux 2.3.41
-The lifetime of orphaned FIN_WAIT2 state sockets.
-This option can be used to override the system-wide setting in the file
-.I /proc/sys/net/ipv4/tcp_fin_timeout
-for this socket.
-This is not to be confused with the
-.BR socket (7)
-level option
-.BR SO_LINGER .
-This option should not be used in code intended to be portable.
-.TP
-.B TCP_MAXSEG
-.\" Present in Linux 1.0
-The maximum segment size for outgoing TCP packets.
-In Linux 2.2 and earlier, and in Linux 2.6.28 and later,
-if this option is set before connection establishment, it also
-changes the MSS value announced to the other end in the initial packet.
-Values greater than the (eventual) interface MTU have no effect.
-TCP will also impose
-its minimum and maximum bounds over the value provided.
-.TP
-.B TCP_NODELAY
-.\" Present in Linux 1.0
-If set, disable the Nagle algorithm.
-This means that segments
-are always sent as soon as possible, even if there is only a
-small amount of data.
-When not set, data is buffered until there
-is a sufficient amount to send out, thereby avoiding the
-frequent sending of small packets, which results in poor
-utilization of the network.
-This option is overridden by
-.BR TCP_CORK ;
-however, setting this option forces an explicit flush of
-pending output, even if
-.B TCP_CORK
-is currently set.
-.TP
-.BR TCP_QUICKACK " (since Linux 2.4.4)"
-Enable quickack mode if set or disable quickack
-mode if cleared.
-In quickack mode, acks are sent
-immediately, rather than delayed if needed in accordance
-to normal TCP operation.
-This flag is not permanent,
-it only enables a switch to or from quickack mode.
-Subsequent operation of the TCP protocol will
-once again enter/leave quickack mode depending on
-internal protocol processing and factors such as
-delayed ack timeouts occurring and data transfer.
-This option should not be used in code intended to be
-portable.
-.TP
-.BR TCP_SYNCNT " (since Linux 2.4)"
-.\" Precisely: since Linux 2.3.18
-Set the number of SYN retransmits that TCP should send before
-aborting the attempt to connect.
-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
-.I 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, or buffered data may remain untransmitted
-(due to zero window size) 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 use the system default.
-.IP
-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.
-.IP
-This option can be set during any state of a TCP connection,
-but is effective only 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.
-.IP
-The option has no effect on when TCP retransmits a packet,
-nor when a keepalive probe is sent.
-.IP
-This option, like many others, will be inherited by the socket returned by
-.BR accept (2),
-if it was set on the listening socket.
-.IP
-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 Linux 2.3.41
-Bound the size of the advertised window to this value.
-The kernel imposes a minimum size of SOCK_MIN_RCVBUF/2.
-This option should not be used in code intended to be
-portable.
-.TP
-.BR TCP_FASTOPEN " (since Linux 3.6)"
-This option enables Fast Open (RFC\~7413) on the listener socket.
-The value specifies the maximum length of pending SYNs
-(similar to the backlog argument in
-.BR listen (2)).
-Once enabled,
-the listener socket grants the TCP Fast Open cookie
-on incoming SYN with TCP Fast Open option.
-.IP
-More importantly it accepts the data in SYN with a valid Fast Open cookie
-and responds SYN-ACK acknowledging both the data and the SYN sequence.
-.BR accept (2)
-returns a socket that is available for read and write
-when the handshake has not completed yet.
-Thus the data exchange can commence before the handshake completes.
-This option requires enabling the server-side support on sysctl
-.I net.ipv4.tcp_fastopen
-(see above).
-For TCP Fast Open client-side support,
-see
-.BR send (2)
-.B MSG_FASTOPEN
-or
-.B TCP_FASTOPEN_CONNECT
-below.
-.TP
-.BR TCP_FASTOPEN_CONNECT " (since Linux 4.11)"
-This option enables an alternative way to perform Fast Open
-on the active side (client).
-When this option is enabled,
-.BR connect (2)
-would behave differently depending on
-if a Fast Open cookie is available for the destination.
-.IP
-If a cookie is not available (i.e. first contact to the destination),
-.BR connect (2)
-behaves as usual by sending a SYN immediately,
-except the SYN would include an empty Fast Open cookie option
-to solicit a cookie.
-.IP
-If a cookie is available,
-.BR connect (2)
-would return 0 immediately but the SYN transmission is deferred.
-A subsequent
-.BR write (2)
-or
-.BR sendmsg (2)
-would trigger a SYN with data plus cookie in the Fast Open option.
-In other words,
-the actual connect operation is deferred until data is supplied.
-.IP
-.B Note:
-While this option is designed for convenience,
-enabling it does change the behaviors and certain system calls might set
-different
-.I errno
-values.
-With cookie present,
-.BR write (2)
-or
-.BR sendmsg (2)
-must be called right after
-.BR connect (2)
-in order to send out SYN+data to complete 3WHS and establish connection.
-Calling
-.BR read (2)
-right after
-.BR connect (2)
-without
-.BR write (2)
-will cause the blocking socket to be blocked forever.
-.IP
-The application should either set
-.B TCP_FASTOPEN_CONNECT
-socket option before
-.BR write (2)
-or
-.BR sendmsg (2),
-or call
-.BR write (2)
-or
-.BR sendmsg (2)
-with
-.B MSG_FASTOPEN
-flag directly,
-instead of both on the same connection.
-.IP
-Here is the typical call flow with this new option:
-.IP
-.in +4n
-.EX
-s = socket();
-setsockopt(s, IPPROTO_TCP, TCP_FASTOPEN_CONNECT, 1, ...);
-connect(s);
-write(s); /* write() should always follow connect()
-           * in order to trigger SYN to go out. */
-read(s)/write(s);
-/* ... */
-close(s);
-.EE
-.in
-.SS Sockets API
-TCP provides limited support for out-of-band data,
-in the form of (a single byte of) urgent data.
-In Linux this means if the other end sends newer out-of-band
-data the older urgent data is inserted as normal data into
-the stream (even when
-.B SO_OOBINLINE
-is not set).
-This differs from BSD-based stacks.
-.P
-Linux uses the BSD compatible interpretation of the urgent
-pointer field by default.
-This violates RFC\ 1122, but is
-required for interoperability with other stacks.
-It can be changed via
-.IR /proc/sys/net/ipv4/tcp_stdurg .
-.P
-It is possible to peek at out-of-band data using the
-.BR recv (2)
-.B MSG_PEEK
-flag.
-.P
-Since Linux 2.4, Linux supports the use of
-.B MSG_TRUNC
-in the
-.I flags
-argument of
-.BR recv (2)
-(and
-.BR recvmsg (2)).
-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,
-.B MSG_TRUNC
-also has this effect when used in conjunction with
-.B MSG_OOB
-to receive out-of-band data.
-.SS Ioctls
-The following
-.BR ioctl (2)
-calls return information in
-.IR value .
-The correct syntax is:
-.P
-.RS
-.nf
-.BI int " value";
-.IB error " = ioctl(" tcp_socket ", " ioctl_type ", &" value ");"
-.fi
-.RE
-.P
-.I ioctl_type
-is one of the following:
-.TP
-.B SIOCINQ
-Returns the amount of queued unread data in the receive buffer.
-The socket must not be in LISTEN state, otherwise an error
-.RB ( EINVAL )
-is returned.
-.B SIOCINQ
-is defined in
-.IR <linux/sockios.h> .
-.\" FIXME https://www.sourceware.org/bugzilla/show_bug.cgi?id=12002,
-.\" filed 2010-09-10, may cause SIOCINQ to be defined in glibc headers
-Alternatively,
-you can use the synonymous
-.BR FIONREAD ,
-defined in
-.IR <sys/ioctl.h> .
-.TP
-.B SIOCATMARK
-Returns true (i.e.,
-.I value
-is nonzero) if the inbound data stream is at the urgent mark.
-.IP
-If the
-.B SO_OOBINLINE
-socket option is set, and
-.B SIOCATMARK
-returns true, then the
-next read from the socket will return the urgent data.
-If the
-.B SO_OOBINLINE
-socket option is not set, and
-.B SIOCATMARK
-returns true, then the
-next read from the socket will return the bytes following
-the urgent data (to actually read the urgent data requires the
-.B recv(MSG_OOB)
-flag).
-.IP
-Note that a read never reads across the urgent mark.
-If an application is informed of the presence of urgent data via
-.BR select (2)
-(using the
-.I exceptfds
-argument) or through delivery of a
-.B SIGURG
-signal,
-then it can advance up to the mark using a loop which repeatedly tests
-.B SIOCATMARK
-and performs a read (requesting any number of bytes) as long as
-.B SIOCATMARK
-returns false.
-.TP
-.B SIOCOUTQ
-Returns the amount of unsent data in the socket send queue.
-The socket must not be in LISTEN state, otherwise an error
-.RB ( EINVAL )
-is returned.
-.B SIOCOUTQ
-is defined in
-.IR <linux/sockios.h> .
-.\" FIXME . https://www.sourceware.org/bugzilla/show_bug.cgi?id=12002,
-.\" filed 2010-09-10, may cause SIOCOUTQ to be defined in glibc headers
-Alternatively,
-you can use the synonymous
-.BR TIOCOUTQ ,
-defined in
-.IR <sys/ioctl.h> .
-.SS Error handling
-When a network error occurs, TCP tries to resend the packet.
-If it doesn't succeed after some time, either
-.B ETIMEDOUT
-or the last received error on this connection is reported.
-.P
-Some applications require a quicker error notification.
-This can be enabled with the
-.B IPPROTO_IP
-level
-.B IP_RECVERR
-socket option.
-When this option is enabled, all incoming
-errors are immediately passed to the user program.
-Use this option with care \[em] it makes TCP less tolerant to routing
-changes and other normal network conditions.
-.SH ERRORS
-.TP
-.B EAFNOTSUPPORT
-Passed socket address type in
-.I sin_family
-was not
-.BR AF_INET .
-.TP
-.B EPIPE
-The other end closed the socket unexpectedly or a read is
-executed on a shut down socket.
-.TP
-.B ETIMEDOUT
-The other end didn't acknowledge retransmitted data after some time.
-.P
-Any errors defined for
-.BR ip (7)
-or the generic socket layer may also be returned for TCP.
-.SH VERSIONS
-Support for Explicit Congestion Notification, zero-copy
-.BR sendfile (2),
-reordering support and some SACK extensions
-(DSACK) were introduced in Linux 2.4.
-Support for forward acknowledgement (FACK), TIME_WAIT recycling,
-and per-connection keepalive socket options were introduced in Linux 2.3.
-.SH BUGS
-Not all errors are documented.
-.P
-IPv6 is not described.
-.\" Only a single Linux kernel version is described
-.\" Info for 2.2 was lost. Should be added again,
-.\" or put into a separate page.
-.\" .SH AUTHORS
-.\" This man page was originally written by Andi Kleen.
-.\" It was updated for 2.4 by Nivedita Singhvi with input from
-.\" Alexey Kuznetsov's Documentation/networking/ip-sysctl.txt
-.\" document.
-.SH SEE ALSO
-.BR accept (2),
-.BR bind (2),
-.BR connect (2),
-.BR getsockopt (2),
-.BR listen (2),
-.BR recvmsg (2),
-.BR sendfile (2),
-.BR sendmsg (2),
-.BR socket (2),
-.BR ip (7),
-.BR socket (7)
-.P
-The kernel source file
-.IR Documentation/networking/ip\-sysctl.txt .
-.P
-RFC\ 793 for the TCP specification.
-.br
-RFC\ 1122 for the TCP requirements and a description of the Nagle algorithm.
-.br
-RFC\ 1323 for TCP timestamp and window scaling options.
-.br
-RFC\ 1337 for a description of TIME_WAIT assassination hazards.
-.br
-RFC\ 3168 for a description of Explicit Congestion Notification.
-.br
-RFC\ 2581 for TCP congestion control algorithms.
-.br
-RFC\ 2018 and RFC\ 2883 for SACK and extensions to SACK.