Netstat
prints information about the Linux networking subsystem. The type of
information printed is controlled by the first argument, as follows:
(none)
By default,
netstat
displays a list of open sockets. If you don't specify any
address families, then the active sockets of all configured address
families will be printed.
--route , -r
Display the kernel routing tables.
--groups , -g
Display multicast group membership information for IPv4 and IPv6.
--interface=iface , -i
Display a table of all network interfaces, or the specified
iface).
--masquerade , -M
Display a list of masqueraded connections.
--statistics , -s
Display summary statistics for each protocol.
OPTIONS
--verbose , -v
Tell the user what is going on by being verbose. Especially print some
useful information about unconfigured address families.
--numeric , -n
Show numerical addresses instead of trying to determine symbolic host, port
or user names.
--numeric-hosts
shows numerical host addresses but does not affect the resolution of
port or user names.
--numeric-ports
shows numerical port numbers but does not affect the resolution of
host or user names.
--numeric-users
shows numerical user IDs but does not affect the resolution of host or
port names.
--protocol=family , -A
Specifies the address families (perhaps better described as low level
protocols) for which connections are to be shown.
family
is a comma (',') separated list of address family keywords like
inet,
unix,
ipx,
ax25,
netrom,
and
ddp.
This has the same effect as using the
--inet,
--unix (-x),
--ipx,
--ax25,
--netrom,
and
--ddp
options.
The address family
inet
includes raw, udp and tcp protocol sockets.
-c, --continuous
This will cause
netstat
to print the selected information every second continuously.
-e, --extend
Display additional information. Use this option twice for maximum detail.
-o, --timers
Include information related to networking timers.
-p, --program
Show the PID and name of the program to which each socket belongs.
-l, --listening
Show only listening sockets. (These are omitted by default.)
-a, --all
Show both listening and non-listening sockets. With the
--interfaces
option, show interfaces that are not marked
-F
Print routing information from the FIB. (This is the default.)
-C
Print routing information from the route cache.
-Z --context
If SELinux enabled print SELinux context.
-T --notrim
Stop trimming long addresses.
delay
Netstat will cycle printing through statistics every
delay
seconds.
UP.
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 acknowledged by the remote host.
Local Address
Address and port number of the local end of the socket. Unless the
--numeric (-n)
option is specified, the socket address is resolved to its canonical
host name (FQDN), and the port number is translated into the
corresponding service name.
Foreign Address
Address and port number of the remote end of the socket.
Analogous to "Local Address."
State
The state of the socket. Since there are no states in raw mode and usually no
states used in UDP, this column 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 has shut down, and the socket is closed. Waiting for
acknowledgement.
LISTEN
The socket is listening for incoming connections. Such sockets are
not included in the output unless you specify the
--listening (-l)
or
--all (-a)
option.
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 username or the user id (UID) of the owner of the socket.
PID/Program name
Slash-separated pair of the process id (PID) and process name of the
process that owns the socket.
--program
causes this column to be included. You will also need
superuser
privileges to see this information on sockets you don't own. 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. Such
sockets are only included in the output if you specify the
--listening (-l)
or
--all (-a)
option.
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
Process ID (PID) and process name of the process that has the socket open.
More info available in
Active Internet connections
section written above.
Path
This is 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
Starting with Linux release 2.2
netstat -i
does not show interface statistics for alias interfaces. 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
-- Mount point for the proc filesystem, which gives access to kernel
status information via the following files.
/proc/net/dev
-- device 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
Occasionally strange information may appear if a socket changes
as it is viewed. This is unlikely to occur.
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 by Bernd Eckenfels
<ecki@linux.de>.
