NETSTAT

NAME
SYNOPSIS
DESCRIPTION
OPTIONS
OUTPUT
NOTES
FILES
SEE ALSO
BUGS
AUTHORS

NAME

netstat − Display network connections, routing tables, interface statistics, masquerade connections, netlink messages, and multicast memberships

SYNOPSIS

netstat [−venaocs] [−−tcp|−t] [−−udp|−u] [−−raw|−w] [−−groups|−g] [−−unix|−x] [−−inet|−−ip] [−−ax25] [−−ipx] [−−netrom]

netstat [−venc] [−−inet] [−−ipx] [−−netrom] [−−ddp] [−−ax25] {−−route|−r}

netstat [−venpac] {−−interfaces|−i} [iface]

netstat [−enc] {−−masquerade|−M}

netstat [−cn] {−−netlink|−L}

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. The address family inet will display raw, udp and tcp sockets.

−a, −−all

The −a, −−all option will print information about all sockets, including the listening server sockets.

−l, −−listening

The −l, −−listening option will print information about listening server sockets only.

−e, −−extend

The −e, −−extend option prints some additional information (e.g. user id and inode of the connection).

−p, −−programs

The −p, −−programs option displays additional information about the program that is using the socket (e.g. process id and the name of the program).

−v, −−verbose

The −v, −−verbose switch makes netstat complain about known address families which are not supported by the kernel.

−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.

−g, −−groups

With the −g, −−groups option, IGMP multicast group membership information for IPv4 and IPv6 is displayed.

−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).

−L, −−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.

−p, −−programs

displays process name and PID of the owner of each socket it dumps. You have to be the owner of such process to have all it’s sockets matched to it or generally root user will see all the necessary information in place.

−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

A connection request has been received from the network.

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 to handle packets still in the network.

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.

PID/Program name

Slash-separated pair of the PID and process name of the program holding this socket. Option -p enables display of this column. You will also need root privileges as you have to have access rights to process to be able to see the program’s sockets matched up to it. This identification information is not yet available for IPX sockets.

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.

PID/Program name

PID and process name of the program holding this socket. More info available in Active Internet connections section written above.

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)

NOTES

Since kernel release 2.2 netstat -i does not display interface statistics for alias interfaces anymore. To get per alias interface counters you need to setup explicit rules using the ipchains(8) command.

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/igmp -- IGMP multicast information

/proc/net/unix -- Unix domain socket information

/proc/net/ipx -- IPX socket information

/proc/net/ax25 -- AX25 socket information

/proc/net/appletalk -- DDP (appletalk) 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) ipchains(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. It was updated again by Tuan Hoang <tqhoang@bigfoot.com>.
The man page and the command included in the net-tools package is totally rewritten from Bernd Eckenfels <ecki@linux.de>.