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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
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