show network status
netstat [-Aan]
netstat [-imnrs]
netstat [-n] [-I [interface]] [-w wait]
netstat [-p protocol]
- -A
- With the default display, show the addresses of any
protocol control blocks associated with sockets.
- -a
- In the default display, show the state of all sockets.
Without -a, sockets used by server processes
aren't shown.
- -d
- With either interface display (-i option or
interval argument), show the number of dropped
packets.
- -I [interface]
- Show information only about this interface. If
interface isn't given, information for all
interfaces will be displayed.
To see how this option is used with the interval
argument, see under the Description below.
- -i
- Show the state of interfaces that have been
auto-configured. Interfaces statically configured into a
system but not located at boot time aren't shown.
- -m
- Show statistics recorded by the memory-management
routines (the network manages a private pool of memory
buffers).
- -n
- Show network addresses as numbers (normally
netstat interprets addresses and attempts to
display them symbolically).
- -p protocol
- Show statistics about protocol, which is
either a well-known name for a protocol or an alias for it.
Some protocol names and aliases are listed in the file
/etc/protocols. A null response typically
means that there are no interesting numbers to report. The
utility will complain if protocol is unknown or
if there's no statistics routine for it.
- -r
- Show the routing tables. When -s is also
present, show routing statistics instead.
- -s
- Show per-protocol statistics.
- -w wait
- Specify the time interval for displaying interface statistics.
The netstat utility displays the contents of
various network-related data structures. It displays in one
of several output formats, depending on the options
selected:
- First form - displays a list of active
sockets for each protocol.
- Second form -displays the contents of one
of the other network data structures, according to the
option selected.
- Third form - with the interval
argument specified, this form continuously displays the
information regarding packet traffic on the configured
network interfaces.
- Fourth form - displays statistics about the
named protocol.
The default display, for active sockets, shows the local and
remote addresses, the send and receive queue sizes (in
bytes), the protocol, and the internal state of the
protocol. If a socket's address specifies a network but no
specific host address, address formats are of the form
host.port or network.port
When known, the host and network addresses are displayed
symbolically according to the databases
/etc/hosts and /etc/networks,
respectively. If a symbolic name for an address is unknown,
or if -n is specified, the address is printed
numerically, according to the address family. For more
information regarding the Internet ``dot format,''
see the inet_*() functions. Unspecified or wildcard
addresses and ports appear as *.
The interface display (-i option or
interval argument) provides a table of cumulative
statistics regarding errors, collisions, and packets
transferred. The network addresses of the interface and the
maximum transmission unit (MTU) are also displayed.
The routing table display (option -r) indicates
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 display includes several
fields:
- flags
- Shows the state of the route:
- D
- The route was created dynamically by a redirect.
- G
- The route uses a gateway.
- H
- The destination is a host.
- M
- The route has been modified by a redirect.
- U
- The route is up.
- gateway
- Direct routes are created for each interface attached to
the local host. For such entries, this field shows the
address of the outgoing interface.
- interface
- Indicates the network interface used for the route.
- refcnt
- 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; connectionless
protocols obtain a route while sending to the same
destination.
- use
- Provides a count of the number of packets sent using the
route.
When netstat is invoked with the
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 auto-configuration) and a column
summarizing information for all interfaces. Using the
-I option, you can replace the primary interface
with another interface. 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.
/etc/hosts file,
/etc/networks file,
/etc/protocols file,
/etc/services file