linux/Documentation/networking/proc_net_tcp.txt
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   1This document describes the interfaces /proc/net/tcp and /proc/net/tcp6.
   2Note that these interfaces are deprecated in favor of tcp_diag.
   3
   4These /proc interfaces provide information about currently active TCP 
   5connections, and are implemented by tcp4_seq_show() in net/ipv4/tcp_ipv4.c
   6and tcp6_seq_show() in net/ipv6/tcp_ipv6.c, respectively.
   7
   8It will first list all listening TCP sockets, and next list all established
   9TCP connections. A typical entry of /proc/net/tcp would look like this (split 
  10up into 3 parts because of the length of the line):
  11
  12   46: 010310AC:9C4C 030310AC:1770 01 
  13   |      |      |      |      |   |--> connection state
  14   |      |      |      |      |------> remote TCP port number
  15   |      |      |      |-------------> remote IPv4 address
  16   |      |      |--------------------> local TCP port number
  17   |      |---------------------------> local IPv4 address
  18   |----------------------------------> number of entry
  19
  20   00000150:00000000 01:00000019 00000000  
  21      |        |     |     |       |--> number of unrecovered RTO timeouts
  22      |        |     |     |----------> number of jiffies until timer expires
  23      |        |     |----------------> timer_active (see below)
  24      |        |----------------------> receive-queue
  25      |-------------------------------> transmit-queue
  26
  27   1000        0 54165785 4 cd1e6040 25 4 27 3 -1
  28    |          |    |     |    |     |  | |  | |--> slow start size threshold, 
  29    |          |    |     |    |     |  | |  |      or -1 if the threshold
  30    |          |    |     |    |     |  | |  |      is >= 0xFFFF
  31    |          |    |     |    |     |  | |  |----> sending congestion window
  32    |          |    |     |    |     |  | |-------> (ack.quick<<1)|ack.pingpong
  33    |          |    |     |    |     |  |---------> Predicted tick of soft clock
  34    |          |    |     |    |     |              (delayed ACK control data)
  35    |          |    |     |    |     |------------> retransmit timeout
  36    |          |    |     |    |------------------> location of socket in memory
  37    |          |    |     |-----------------------> socket reference count
  38    |          |    |-----------------------------> inode
  39    |          |----------------------------------> unanswered 0-window probes
  40    |---------------------------------------------> uid
  41
  42timer_active:
  43  0  no timer is pending
  44  1  retransmit-timer is pending
  45  2  another timer (e.g. delayed ack or keepalive) is pending
  46  3  this is a socket in TIME_WAIT state. Not all fields will contain 
  47     data (or even exist)
  48  4  zero window probe timer is pending
  49
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