1.. SPDX-License-Identifier: GPL-2.0 2 3============================================ 4The proc/net/tcp and proc/net/tcp6 variables 5============================================ 6 7This document describes the interfaces /proc/net/tcp and /proc/net/tcp6. 8Note that these interfaces are deprecated in favor of tcp_diag. 9 10These /proc interfaces provide information about currently active TCP 11connections, and are implemented by tcp4_seq_show() in net/ipv4/tcp_ipv4.c 12and tcp6_seq_show() in net/ipv6/tcp_ipv6.c, respectively. 13 14It will first list all listening TCP sockets, and next list all established 15TCP connections. A typical entry of /proc/net/tcp would look like this (split 16up into 3 parts because of the length of the line):: 17 18 46: 010310AC:9C4C 030310AC:1770 01 19 | | | | | |--> connection state 20 | | | | |------> remote TCP port number 21 | | | |-------------> remote IPv4 address 22 | | |--------------------> local TCP port number 23 | |---------------------------> local IPv4 address 24 |----------------------------------> number of entry 25 26 00000150:00000000 01:00000019 00000000 27 | | | | |--> number of unrecovered RTO timeouts 28 | | | |----------> number of jiffies until timer expires 29 | | |----------------> timer_active (see below) 30 | |----------------------> receive-queue 31 |-------------------------------> transmit-queue 32 33 1000 0 54165785 4 cd1e6040 25 4 27 3 -1 34 | | | | | | | | | |--> slow start size threshold, 35 | | | | | | | | | or -1 if the threshold 36 | | | | | | | | | is >= 0xFFFF 37 | | | | | | | | |----> sending congestion window 38 | | | | | | | |-------> (ack.quick<<1)|ack.pingpong 39 | | | | | | |---------> Predicted tick of soft clock 40 | | | | | | (delayed ACK control data) 41 | | | | | |------------> retransmit timeout 42 | | | | |------------------> location of socket in memory 43 | | | |-----------------------> socket reference count 44 | | |-----------------------------> inode 45 | |----------------------------------> unanswered 0-window probes 46 |---------------------------------------------> uid 47 48timer_active: 49 50 == ================================================================ 51 0 no timer is pending 52 1 retransmit-timer is pending 53 2 another timer (e.g. delayed ack or keepalive) is pending 54 3 this is a socket in TIME_WAIT state. Not all fields will contain 55 data (or even exist) 56 4 zero window probe timer is pending 57 == ================================================================ 58