The proc/net/tcp and proc/net/tcp6 variables

This document describes the interfaces /proc/net/tcp and /proc/net/tcp6.Note that these interfaces are deprecated in favor of tcp_diag.

These /proc interfaces provide information about currently active TCPconnections, and are implemented by tcp4_seq_show() in net/ipv4/tcp_ipv4.cand tcp6_seq_show() in net/ipv6/tcp_ipv6.c, respectively.

It will first list all listening TCP sockets, and next list all establishedTCP connections. A typical entry of /proc/net/tcp would look like this (splitup into 3 parts because of the length of the line):

46: 010310AC:9C4C 030310AC:1770 01|      |      |      |      |   |--> connection state|      |      |      |      |------> remote TCP port number|      |      |      |-------------> remote IPv4 address|      |      |--------------------> local TCP port number|      |---------------------------> local IPv4 address|----------------------------------> number of entry00000150:00000000 01:00000019 00000000   |        |     |     |       |--> number of unrecovered RTO timeouts   |        |     |     |----------> number of jiffies until timer expires   |        |     |----------------> timer_active (see below)   |        |----------------------> receive-queue   |-------------------------------> transmit-queue1000        0 54165785 4 cd1e6040 25 4 27 3 -1 |          |    |     |    |     |  | |  | |--> slow start size threshold, |          |    |     |    |     |  | |  |      or -1 if the threshold |          |    |     |    |     |  | |  |      is >= 0xFFFF |          |    |     |    |     |  | |  |----> sending congestion window |          |    |     |    |     |  | |-------> (ack.quick<<1)|ack.pingpong |          |    |     |    |     |  |---------> Predicted tick of soft clock |          |    |     |    |     |              (delayed ACK control data) |          |    |     |    |     |------------> retransmit timeout |          |    |     |    |------------------> location of socket in memory |          |    |     |-----------------------> socket reference count |          |    |-----------------------------> inode |          |----------------------------------> unanswered 0-window probes |---------------------------------------------> uid

timer_active:

0no timer is pending
1retransmit-timer is pending
2another timer (e.g. delayed ack or keepalive) is pending
3this is a socket in TIME_WAIT state. Not all fields will containdata (or even exist)
4zero window probe timer is pending