NETSTAT(8)

NAME
netstat - Display network connections, routing tables, interface statistics, masquerade connections and netlink messages

SYNOPSIS
netstat [-venaoc] [--tcp|-t] [--udp|-u] [--raw|-w] [--unix|-x] [--inet|--ip] [--ax25] [--ipx] [--netrom]

netstat [-veenc] [--inet] [--ipx] [--netrom] [--ddp] [--ax25] {--route|-r}

netstat [-veenac] {--interfaces|-i} [iface]

netstat [-enc] {--masquerade|-M}

netstat [-cn] {--netlink|-N}

netstat {-V|--version} {-h|--help}

DESCRIPTION
Netstat displays information of the Linux networking subsystem.

  (no option)
You can view the status of network connections by listing the open sockets. This is the default operation: If you don't specify any address families, then the active sockets of all configured address families will be printed. With -e you get some additional informations (userid). With the -v switch you can make netstat complain about known address families which are not supported by the kernel. The -o option displays some additional information on networking timers. -a print all sockets, including the listening server sockets. The address family inet will display raw, udp and tcp sockets.

  -r, --route
With the -r, --route option, you get the kernel routing tables in the same format as route -e use. netstat -er will use the output format of route. Please see route(8) for details.

  -i, --interface iface
If you use the -i, --interfaces option, a table of all (or the specified iface) networking interfaces will be printed. The output uses the ifconfig -e format, and is described in ifconfig(8). netstat -ei will print a table or a single interface entry just like ifconfig does. With the -a switch, you can include interfaces which are not configured (i.e. don't have the U=UP flag set).

  -M, --masquerade
A list of all masqueraded sessions can be viewed, too. With the -e switch you can include some more informations about sequenze numbering and deltas, caused by data rewrites on FTP sessions (PORT command). Masquerade support is used to hide hosts with unofficial network addresses from the outside world, as described in ipfw(4),ipfwadm(8) and ipfw(8).

  -N, --netlink
Recent kernels have a kernel/user communication support called netlink. You can get messages about creation or deletion of interfaces or routes from /dev/route (36,0).

OPTIONS

  -v, --verbose
Tell the user what is going on by being verbose. Especially print some usefull informations about unconfigured address families.

  -n, --numeric
shows numerical addresses instead of trying to determine symbolic host, port or user names.

  -A, --af family
use a different method to set the address families. family is a comma (',') seperated list of address family keywords like inet, unix, ipx, ax25, netrom and ddp. This is has the same effect as using the long options --inet, --unix, --ipx, --ax25, --netrom and --ddp.

  -c, --continous
This will cause netstat to print the selected table every second continously on the screen until you interrupt it.

OUTPUT

  Active Internet connections (TCP, UDP, RAW)

  Proto
The protocol (tcp, udp, raw) used by the socket.

  Recv-Q
The count of bytes not copied by the user program connected to this socket.

  Send-Q
The count of bytes not acknoledged by the remote host.

  Local Address
The local address (local hostname) and port number of the socket. Unless the -n switch is given, the socket address is resolved to its canonical hostname, and the port number is translated into the corresponding service name.

  Foreign Address
The remote address (remote hostname) and port number of he socket. As with the local address:port, the -n switch turns off hostname and service name resolution.

  State
The state of the socket. Since there are no states in RAW and usually no states used in UDP, this row may be left blank. Normally this can be one of several values:

ESTABLISHED
    The socket has an established connection.

SYN_SENT
    The socket is actively attempting to establish a connection.

SYN_RECV
    The connection is being initialized.

FIN_WAIT1
    The socket is closed, and the connection is shutting down.

FIN_WAIT2
    Connection is closed, and the socket is waiting for a shutdown from the remote end.

TIME_WAIT
    The socket is waiting after close for remote shutdown retransmission.

CLOSED
    The socket is not being used.

CLOSE_WAIT
    The remote end has shut down, waiting for the socket to close.

LAST_ACK
    The remote end shut down, and the socket is closed. Waiting for acknowledgement.

LISTEN
    The socket is listening for incoming connections. Those sockets are only displayed if the -a,--listening switch is set.

CLOSING
    Both sockets are shut down but we still don't have all our data sent.

UNKNOWN
    The state of the socket is unknown.

  User
The name or the UID of the owner of the socket.

  Timer
(this needs to be written)

  Active UNIX domain Sockets

  Proto
The protocol (usually unix) used by the socket.

  RefCnt
The reference count (i.e. attached processes via this socket).

  Flags
The flags displayed is SO_ACCEPTON (displayed as ACC), SO_WAITDATA (W) or SO_NOSPACE (N). SO_ACCECPTON is used on unconnected sockets if their corresponding processes are waiting for a connect request. The other flags are not of normal interest.

  Type
There are several types of socket access:

SOCK_DGRAM
    The socket is used in Datagram (connectionless) mode.

SOCK_STREAM
    This is a stream (connection) socket.

SOCK_RAW
    The socket is used as a raw socket.

SOCK_RDM
    This one serves reliably-delivered messages.

SOCK_SEQPACKET
    This is a sequential packet socket.

SOCK_PACKET
    RAW interface access socket.

UNKNOWN
    Who ever knows, what the future will bring us - just fill in here :-)

  State
This field will contain one of the following Keywords:

FREE
    The socket is not allocated

LISTENING
    The socket is listening for a connection request. Those sockets are only displayed if the -a,--listening switch is set.

CONNECTING
    The socket is about to establish a connection.

CONNECTED
    The socket is connected.

DISCONNECTING
    The socket is disconnecting.

(empty)
    The socket is not connected to another one.

UNKNOWN
    This state should never happen.

  Path
This displays the path name as which the corresponding processes attached to the socket.

  Active IPX sockets
(this needs to be done by somebody who knows it)

  Active NET/ROM sockets
(this needs to be done by somebody who knows it)

  Active AX.25 sockets
(this needs to be done by somebody who knows it)

FILES
/etc/services -- The services translation file /proc/net/dev -- devices information /proc/net/raw -- RAW socket information /proc/net/tcp -- TCP socket information /proc/net/udp -- UDP socket information /proc/net/unix -- Unix domain socket information /proc/net/ipx -- IPX socket information /proc/net/ax25 -- AX25 socket information /proc/net/appeltalk -- DDP (appeltalk) socket information /proc/net/nr -- NET/ROM socket information /proc/net/route -- Kernel IP routing information /proc/net/ax25_route -- Kernel AX25 routing information /proc/net/ipx_route -- Kernel IPX routing information /proc/net/nr_nodes -- Kernel NET/ROM nodelist /proc/net/nr_neigh -- Kernel NET/ROM neighbours /proc/net/ip_masquerade -- Kernel masqueraded connections

SEE ALSO
route(8), ifconfig(8), ipfw(4), ipfw(8), ipfwadm(8)

BUGS
Occasionally strange information may appear if a socket changes as it is viewed. This is unlikely to occur.
The netstat -i options is described as it should work after some code cleanup of the BETA release of the net-tools package.

AUTHORS
The netstat user interface was written by Fred Baumgarten <dc6iq@insu1.etec.uni-karlsruhe.de> the man page basically by Matt Welsh <mdw@tc.cornell.edu>. It was updated by Alan Cox <Alan.Cox@linux.org> but could do with a bit more work.
The man page and the command included in the net-tools package is totally rewritten from Bernd Eckenfels <ecki@linux.de>.