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Full Discussion: netstat
Operating Systems Linux Red Hat netstat Post 302779201 by Praveen_218 on Tuesday 12th of March 2013 10:20:32 AM
Old 03-12-2013
They are TCP-states only!!!

If an application using STREAM sockets; tcp protocol thread serve them and each such thread, at any point in time during the socket operations, has an state out of a total of 11 defined TCP states, based on the phase of the communication. This includes the beginning (right from the 1st SYN in the 3-way handshake) to the termination of the communication (when you close a socket).

The 'netstat' shows these states of all the TCP threads serving their corresponding sockets.

Please look at RFC#793.

Attaching the text showing TCP state change diagram.
The diagram depicts the states a TCP thread under goes (taken from RFC#793).

Last edited by Praveen_218; 03-12-2013 at 11:32 AM.. Reason: Pasting the diagram text directly didn't work well, hence uploaded the text file.
 

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SS(8)							      System Manager's Manual							     SS(8)

NAME
ss - another utility to investigate sockets SYNOPSIS
ss [options] [ FILTER ] DESCRIPTION
ss is used to dump socket statistics. It allows showing information similar to netstat. It can display more TCP and state informations than other tools. OPTIONS
These programs follow the usual GNU command line syntax, with long options starting with two dashes (`-'). A summary of options is included below. -h, --help Show summary of options. -V, --version Output version information. -n, --numeric Do now try to resolve service names. -r, --resolve Try to resolve numeric address/ports. -a, --all Display all sockets. -l, --listening Display listening sockets. -o, --options Show timer information. -e, --extended Show detailed socket information -m, --memory Show socket memory usage. -p, --processes Show process using socket. -i, --info Show internal TCP information. -s, --summary Print summary statistics. This option does not parse socket lists obtaining summary from various sources. It is useful when amount of sockets is so huge that parsing /proc/net/tcp is painful. -4, --ipv4 Display only IP version 4 sockets (alias for -f inet). -6, --ipv6 Display only IP version 6 sockets (alias for -f inet6). -0, --packet Display PACKET sockets. -t, --tcp Display only TCP sockets. -u, --udp Display only UDP sockets. -d, --dccp Display only DCCP sockets. -w, --raw Display only RAW sockets. -x, --unix Display only Unix domain sockets. -f FAMILY, --family=FAMILY Display sockets of type FAMILY. Currently the following families are supported: unix, inet, inet6, link, netlink. -A QUERY, --query=QUERY List of socket tables to dump, separated by commas. The following identifiers are understood: all, inet, tcp, udp, raw, unix, packet, netlink, unix_dgram, unix_stream, packet_raw, packet_dgram. -D FILE Do not display anything, just dump raw information about TCP sockets to FILE after applying filters. If FILE is - stdout is used. -F FILE, --filter=FILE Read filter information from FILE. Each line of FILE is interpreted like single command line option. If FILE is - stdin is used. FILTER := [ state TCP-STATE ] [ EXPRESSION ] Please take a look at the official documentation (Debian package iproute-doc) for details regarding filters. USAGE EXAMPLES
ss -t -a Display all TCP sockets. ss -u -a Display all UDP sockets. ss -o state established '( dport = :ssh or sport = :ssh )' Display all established ssh connections. ss -x src /tmp/.X11-unix/* Find all local processes connected to X server. ss -o state fin-wait-1 '( sport = :http or sport = :https )' dst 193.233.7/24 List all the tcp sockets in state FIN-WAIT-1 for our apache to network 193.233.7/24 and look at their timers. SEE ALSO
ip(8), /usr/share/doc/iproute-doc/ss.html (package iproutedoc) AUTHOR
ss was written by Alexey Kuznetosv, <kuznet@ms2.inr.ac.ru>. This manual page was written by Michael Prokop <mika@grml.org> for the Debian project (but may be used by others). SS(8)
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