Netstat command displays various network related information such as network connections, routing tables, interface statistics, masquerade connections, multicast memberships etc.,
In this article, let us review 10 practical unix netstat command examples.
1. List All Ports (both listening and non listening ports)
List all ports using netstat -a
# netstat -a | more
Active Internet connections (servers and established)
Proto Recv-Q Send-Q Local Address Foreign Address State
tcp 0 0 localhost:30037 *:* LISTEN
udp 0 0 *:bootpc *:*
Active UNIX domain sockets (servers and established)
Proto RefCnt Flags Type State I-Node Path
unix 2 [ ACC ] STREAM LISTENING 6135 /tmp/.X11-unix/X0
unix 2 [ ACC ] STREAM LISTENING 5140 /var/run/acpid.socket
List all tcp ports using netstat -at
# netstat -at Active Internet connections (servers and established) Proto Recv-Q Send-Q Local Address Foreign Address State tcp 0 0 localhost:30037 *:* LISTEN tcp 0 0 localhost:ipp *:* LISTEN tcp 0 0 *:smtp *:* LISTEN tcp6 0 0 localhost:ipp [::]:* LISTEN
List all udp ports using netstat -au
# netstat -au Active Internet connections (servers and established) Proto Recv-Q Send-Q Local Address Foreign Address State udp 0 0 *:bootpc *:* udp 0 0 *:49119 *:* udp 0 0 *:mdns *:*
2. List Sockets which are in Listening State
List only listening ports using netstat -l
# netstat -l Active Internet connections (only servers) Proto Recv-Q Send-Q Local Address Foreign Address State tcp 0 0 localhost:ipp *:* LISTEN tcp6 0 0 localhost:ipp [::]:* LISTEN udp 0 0 *:49119 *:*
List only listening TCP Ports using netstat -lt
# netstat -lt Active Internet connections (only servers) Proto Recv-Q Send-Q Local Address Foreign Address State tcp 0 0 localhost:30037 *:* LISTEN tcp 0 0 *:smtp *:* LISTEN tcp6 0 0 localhost:ipp [::]:* LISTEN
List only listening UDP Ports using netstat -lu
# netstat -lu Active Internet connections (only servers) Proto Recv-Q Send-Q Local Address Foreign Address State udp 0 0 *:49119 *:* udp 0 0 *:mdns *:*
List only the listening UNIX Ports using netstat -lx
# netstat -lx Active UNIX domain sockets (only servers) Proto RefCnt Flags Type State I-Node Path unix 2 [ ACC ] STREAM LISTENING 6294 private/maildrop unix 2 [ ACC ] STREAM LISTENING 6203 public/cleanup unix 2 [ ACC ] STREAM LISTENING 6302 private/ifmail unix 2 [ ACC ] STREAM LISTENING 6306 private/bsmtp
3. Show the statistics for each protocol
Show statistics for all ports using netstat -s
# netstat -s
Ip:
11150 total packets received
1 with invalid addresses
0 forwarded
0 incoming packets discarded
11149 incoming packets delivered
11635 requests sent out
Icmp:
0 ICMP messages received
0 input ICMP message failed.
Tcp:
582 active connections openings
2 failed connection attempts
25 connection resets received
Udp:
1183 packets received
4 packets to unknown port received.
.....
Show statistics for TCP (or) UDP ports using netstat -st (or) -su
# netstat -st # netstat -su
4. Display PID and program names in netstat output using netstat -p
netstat -p option can be combined with any other netstat option. This will add the “PID/Program Name” to the netstat output. This is very useful while debugging to identify which program is running on a particular port.
# netstat -pt Active Internet connections (w/o servers) Proto Recv-Q Send-Q Local Address Foreign Address State PID/Program name tcp 1 0 ramesh-laptop.loc:47212 192.168.185.75:www CLOSE_WAIT 2109/firefox tcp 0 0 ramesh-laptop.loc:52750 lax:www ESTABLISHED 2109/firefox
5. Don’t resolve host, port and user name in netstat output
When you don’t want the name of the host, port or user to be displayed, use netstat -n option. This will display in numbers, instead of resolving the host name, port name, user name.
This also speeds up the output, as netstat is not performing any look-up.
# netstat -an
If you don’t want only any one of those three items ( ports, or hosts, or users ) to be resolved, use following commands.
# netsat -a --numeric-ports # netsat -a --numeric-hosts # netsat -a --numeric-users
6. Print netstat information continuously
netstat will print information continuously every few seconds.
# netstat -c Active Internet connections (w/o servers) Proto Recv-Q Send-Q Local Address Foreign Address State tcp 0 0 ramesh-laptop.loc:36130 101-101-181-225.ama:www ESTABLISHED tcp 1 1 ramesh-laptop.loc:52564 101.11.169.230:www CLOSING tcp 0 0 ramesh-laptop.loc:43758 server-101-101-43-2:www ESTABLISHED tcp 1 1 ramesh-laptop.loc:42367 101.101.34.101:www CLOSING
7. Find the non supportive Address families in your system
netstat --verbose
At the end, you will have something like this.
netstat: no support for `AF IPX' on this system. netstat: no support for `AF AX25' on this system. netstat: no support for `AF X25' on this system. netstat: no support for `AF NETROM' on this system.
8. Display the kernel routing information using netstat -r
# netstat -r Kernel IP routing table Destination Gateway Genmask Flags MSS Window irtt Iface 192.168.1.0 * 255.255.255.0 U 0 0 0 eth2 link-local * 255.255.0.0 U 0 0 0 eth2 default 192.168.1.1 0.0.0.0 UG 0 0 0 eth2
Note: Use netstat -rn to display routes in numeric format without resolving for host-names.
9. Find out on which port a program is running
# netstat -ap | grep ssh (Not all processes could be identified, non-owned process info will not be shown, you would have to be root to see it all.) tcp 1 0 dev-db:ssh 101.174.100.22:39213 CLOSE_WAIT - tcp 1 0 dev-db:ssh 101.174.100.22:57643 CLOSE_WAIT -
Find out which process is using a particular port:
# netstat -an | grep ':80'
10. Show the list of network interfaces
# netstat -i Kernel Interface table Iface MTU Met RX-OK RX-ERR RX-DRP RX-OVR TX-OK TX-ERR TX-DRP TX-OVR Flg eth0 1500 0 0 0 0 0 0 0 0 0 BMU eth2 1500 0 26196 0 0 0 26883 6 0 0 BMRU lo 16436 0 4 0 0 0 4 0 0 0 LRU
Display extended information on the interfaces (similar to ifconfig) using netstat -ie:
# netstat -ie
Kernel Interface table
eth0 Link encap:Ethernet HWaddr 00:10:40:11:11:11
UP BROADCAST MULTICAST MTU:1500 Metric:1
RX packets:0 errors:0 dropped:0 overruns:0 frame:0
TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:0 (0.0 B) TX bytes:0 (0.0 B)
Memory:f6ae0000-f6b00000