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
