Name

netstat − show network status

Syntax

netstat [ −Aan ] [ −f address_family ] [ system ] [ core ]
netstat [ −himnrs ] [ −f address_family ] [ system ] [ core ]
netstat [ −n ] [ −I interface ] interval [ system ] [ core ]
netstat [ −I interface −s ] [ system ] [ core ]

Description

The netstat command displays the contents of network-related data structures symbolically. Depending on the options supplied to netstat, there are a number of output formats.

The first form of the command displays a list of active sockets for each protocol.  The second form presents the contents of one of the other network data structures according to the option selected.  The third form, with an interval specified, continuously displays the information regarding packet traffic on the configured network interfaces.  The fourth form displays the Digital Network Architecture (DNA) Ethernet Data Link Layer counters for an Ethernet interface, or the DNA Fiber Distributed Data Interface (FDDI) Data Link Layer counters for an FDDI interface. It also presents the FDDI adapter’s status and characteristics for the FDDI interface. 

If no options are specified, netstat displays the state of all active sockets from those using any of the protocols listed in /etc/protocols.

The arguments, system and core allow substitutes for the defaults /vmunix and /dev/kmem.

If an interval is specified, netstat display the information regarding packet traffic on the configured network interfaces continuously, pausing interval seconds before refreshing the screen. 

There are a number of display formats, depending on the information presented.  The default display, for active sockets, shows the local and remote addresses, send and receive queue sizes (in bytes), protocol, and, optionally, the internal state of the protocol. 

Address formats are either of the form host.port or network.port, if a socket’s address specifies a network but no specific host address.  When known, the host and network addresses are displayed symbolically according to the data bases /etc/hosts and /etc/networks, respectively.  If a symbolic name for an address is unknown, or if the −n option is specified, the address is printed in the Internet dot format.  Refer to inet() for more information regarding this format. Unspecified, or wildcard, addresses and ports appear as an asterisk (*).

The interface display provides a table of cumulative statistics regarding packets transferred, errors, and collisions.  The network address (currently Internet specific) of the interface and the maximum transmission unit (mtu) are also displayed. 

The routing table display indicates the available routes and their status.  Each route consists of a destination host or network and a gateway to use in forwarding packets.  The flags field shows the state of the route (for example, 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 field gives the current number of active uses of the route.  Connection oriented protocols normally hold on to a single route for the duration of a connection, while connectionless protocols obtain a route while sending to the same destination.  The use field provides a count of the number of packets sent using that route.  The interface entry indicates the network interface utilized for the route. 

When netstat is invoked with an interval argument, it displays a running count of statistics related to network interfaces.  This display consists of a column for the primary interface (the first interface found during autoconfiguration), and a column summarizing information for all interfaces.  The primary interface may be replaced with another interface with the −I option.  The first line of each screen of information contains a summary since the system was last rebooted.  Subsequent lines of output show values accumulated over the preceding interval. 

Options

−ADisplays the address of any associated protocol control blocks; used for debugging. 

−aDisplays the information for all sockets.  Normally sockets used by server processes are not shown. 

−f address_familyLimits statistics or address control block reports to those of the specified address family.  Recognized address families are inet, for AF_INET, and unix, for AF_UNIX. 

−hDisplays the state of the IMP host table. 

−I interfaceShows information only about this interface.  Used with an interval displayed below. 

−I interface -sDisplays the DNA Ethernet Data Link Layer counters for an Ethernet interface.  Displays the DNA FDDI Data Link Layer counters, adapter’s status and characteristics for an FDDI interface. 

−iDisplays status information for autoconfigured interfaces .  Interfaces statically configured into a system, but not located at boot time are not shown. 

−mDisplays information for the memory management routines The network manages a private share of memory. 

−nDisplays network addresses as numbers.  Normally netstat interprets addresses and attempts to display them symbolically.

−rDisplays the routing tables.  When −s is also present, shows routing statistics instead. 

−sDisplays per-protocol statistics. 

−tDisplays time until interface watchdog routine starts up (used only in conjunction with −i option). 

See Also

iostat(1), vmstat(1), hosts(5), networks(5), protocols(5), services(5), trpt(8c)