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Manual page for NETSTAT(8C)

netstat - show network status

SYNOPSIS

netstat [ -aAn ] [ -f address_family ] [ system ] [ core ]

netstat [ -n ] [ -s ] [ -m | -i | -r ] [ -f address_family ] [ system ] [ core ]

netstat [ -n ] [ -I interface ] interval [ system ] [ core ]

AVAILABILITY

This program is available with the Networking software installation option. Refer to [a manual with the abbreviation INSTALL] for information on how to install optional software.

DESCRIPTION

netstat displays the contents of various network-related data structures in various formats, depending on the options you select.

The first form of the command displays a list of active sockets for each protocol. The second form selects one from among various other network data structures. The third form displays running statistics of packet traffic on configured network interfaces; the interval argument indicates the number of seconds in which to gather statistics between displays.

The default value for the system argument is /vmunix; for core, the default is /dev/kmem.

OPTIONS

-a: Show the state of all sockets; normally sockets used by server processes are not shown.
-A: Show the address of any protocol control blocks associated with sockets; used for debugging.
-f address_family: Limit statistics or address control block reports to those of the specified address_family, which can be one of:

inet: For the AF_INET address family, or
unix: For the AF_UNIX family.

-i: Show the state of interfaces that have been auto-configured. Interfaces that are statically configured into a system, but not located at boot time, are not shown.
-I interface: Highlight information about the indicated interface in a separate column; the default (for the third form of the command) is the interface with the most traffic since the system was last rebooted. interface can be any valid interface listed in the system configuration file, such as ie0 or le0.
-m: Show the statistics recorded by management routines for the network's private buffer pool.
-n: Show network addresses as numbers. netstat normally displays addresses as symbols. This option may be used with any of the display formats.
-r: Show the routing tables. (When -s is also present, show routing statistics instead.)
-s: Show per-protocol statistics. When used with the -r option, show routing statistics.
-t: Replace queue length information with timer information.

DISPLAYS

Active Sockets (First Form)

The display for each active socket shows the local and remote address, the send and receive queue sizes (in bytes), the protocol, and the internal state of the protocol.

The symbolic format normally used to display socket addresses is either:

: hostname.port

when the name of the host is specified, or:

: network.port

if a socket address specifies a network but no specific host. Each hostname and network is shown according to its entry in the /etc/hosts or the /etc/networks file, as appropriate.

If the network or hostname for an address is not known (or if the -n option is specified), the numerical network address is shown. Unspecified, or ``wildcard'', addresses and ports appear as ``*''. (For more information regarding the Internet naming conventions, refer to inet.3n

TCP Sockets

The possible state values for TCP sockets are as follows:

CLOSED: Closed: the socket is not being used.
LISTEN: Listening for incoming connections.
SYN_SENT: Actively trying to establish connection.
SYN_RECEIVED: Initial synchronization of the connection under way.
ESTABLISHED: Connection has been established.
CLOSE_WAIT: Remote shut down: waiting for the socket to close.
FIN_WAIT_1: Socket closed, shutting down connection.
CLOSING: Closed, then remote shutdown: awaiting acknowledgement.
LAST_ACK: Remote shut down, then closed: awaiting acknowledgement.
FIN_WAIT_2: Socket closed, waiting for shutdown from remote.
TIME_WAIT: Wait after close for remote shutdown retransmission.

Network Data Structures (Second Form)

The form of the display depends upon which of the -m, -i, -h or -r, options you select. (If you specify more than one of these options, netstat selects one in the order listed here.)

Routing Table Display

The routing table display lists the available routes and the status of each. Each route consists of a destination host or network, and a gateway to use in forwarding packets. The flags column shows the status of the route (U if ``up''), whether the route is to a gateway (G), and whether the route was created dynamically by a redirect (D).

Direct routes are created for each interface attached to the local host; the gateway field for such entries shows the address of the outgoing interface.

The refcnt column gives the current number of active uses per route. (Connection-oriented protocols normally hold on to a single route for the duration of a connection, whereas connectionless protocols obtain a route while sending to the same destination.)

The use column displays the number of packets sent per route.

The interface entry indicates the network interface utilized for the route.

Cumulative Traffic Statistics (Third Form)

When the interval argument is given, netstat displays a table of cumulative statistics regarding packets transferred, errors and collisions, the network addresses for the interface, and the maximum transmission unit (``mtu''). The first line of data displayed, and every 24th line thereafter, contains cumulative statistics from the time the system was last rebooted. Each subsequent line shows incremental statistics for the interval (specified on the command line) since the previous display.

BUGS

The notion of errors is ill-defined. Collisions mean something else for the IMP.

The kernel's tables can change while netstat is examining them, creating incorrect or partial displays.