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 TCP connections, and are implemented by tcp4_seq_show() in net/ipv4/tcp_ipv4.c and tcp6_seq_show() in net/ipv6/tcp_ipv6.c, respectively. It will first list all listening TCP sockets, and next list all established TCP connections. A typical entry of /proc/net/tcp would look like this (split up 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 entry 00000150:00000000 01:00000019 00000000 | | | | |--> number of unrecovered RTO timeouts | | | |----------> number of jiffies until timer expires | | |----------------> timer_active (see below) | |----------------------> receive-queue |-------------------------------> transmit-queue 1000 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: 0 no timer is pending 1 retransmit-timer is pending 2 another timer (e.g. delayed ack or keepalive) is pending 3 this is a socket in TIME_WAIT state. Not all fields will contain data (or even exist) 4 zero window probe timer is pending