netstat – Print network connections, routing tables, interface statistics, masquerade connections, and multicast memberships. Its really good stuff!
netstat [address_family_options] [–tcp|-t] [–udp|-u] [–raw|-w] [–listening|-l] [–all|-a] [–numeric|-n] [–numeric-hosts][–numeric-ports][–numeric-ports] [–symbolic|-N] [–extend|-e[–extend|-e]] [–timers|-o] [–program|-p] [–verbose|-v] [–continuous|-c][delay]
netstat {–route|-r} [address_family_options] [–extend|-e[–extend|-e]] [–verbose|-v] [–numeric|-n] [–numeric-hosts][–numeric-ports][–numeric-ports] [–continuous|-c][delay]
netstat {–interfaces|-I|-i} [iface] [–all|-a] [–extend|-e] [–verbose|-v] [–program|-p] [–numeric|-n] [–numeric-hosts][–numeric-ports][–numeric-ports] [–continuous|-c][delay]
netstat {–groups|-g} [–numeric|-n] [–numeric-hosts][–numeric-ports][–numeric-ports] [–continuous|-c] [delay]
netstat {–masquerade|-M} [–extend|-e] [–numeric|-n] [–numeric-hosts][–numeric-ports][–numeric-ports] [–continuous|-c] [delay]
netstat {–statistics|-s} [–tcp|-t] [–udp|-u] [–raw|-w] [delay]
netstat {–version|-V}
netstat {–help|-h}
address_family_options:
[–protocol={inet,unix,ipx,ax25,netrom,ddp}[,…]] [–unix|-x] [–inet|–ip] [–ax25] [–ipx] [–netrom] [–ddp]
Note
This program is obsolete. Replacement for netstat is ss. Replacement for netstat -r is ip route. Replacement for netstat -i is ip -s link. Replacement for netstat -g is ip maddr.
Description
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.
–interfaces=iface , -I=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 (for TCP this means established connections) 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 superuserprivileges 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 theipchains(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
/proc/net/nr — NET/ROM socket information
/proc/net/route — IP routing information
/proc/net/ax25_route — AX25 routing information
/proc/net/ipx_route — IPX routing information
/proc/net/nr_nodes — NET/ROM nodelist
/proc/net/nr_neigh — NET/ROM neighbours
/proc/net/ip_masquerade — masqueraded connections
/proc/net/snmp — statistics
