netstat [ -n ] [ -s ] [ -m | -i | -r ] [ -f address_family ] [ system ] [ core ]
netstat [ -n ] [ -I interface ] interval [ system ] [ core ]
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.
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:
when the name of the host is specified, or:
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
The possible state values for TCP sockets are as follows:
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.)
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.
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.
The kernel's tables can change while netstat is examining them, creating incorrect or partial displays.
Created by unroff & hp-tools. © by Hans-Peter Bischof. All Rights Reserved (1997).
Last modified 21/April/97