1) From
the man page, "By default, netstat displays a list of open sockets".
Running the netstat command without any arguments on my Linux machine,
[~]
netstat
Active Internet connections (w/o servers)
Proto Recv-Q Send-Q Local
Address
Foreign Address
State
tcp
0 0
user:41236
si-in-f188.1e10:hpvroom ESTABLISHED
tcp
0 0
user:46348
bom05s15-in-f10.1:https ESTABLISHED
tcp
0 0
user:51426
https-111-119-15-:https ESTABLISHED
udp
0 0
user:bootpc
_gateway:bootps
ESTABLISHED
udp
0 0
user:53693
bom07s24-in-f10.1:https ESTABLISHED
Active UNIX domain sockets (w/o servers)
Proto RefCnt Flags
Type
State
I-Node Path
unix 2 [
]
DGRAM
27060 /run/user/1000/systemd/notify
unix 2 [
]
DGRAM
27806 /run/wpa_supplicant/wlan0
...
2) Get summary statistics for each protocol(UDP, TCP, ICMP, IP), using the statistics flag(--statistics or simply -s)
~]
netstat
-s
Ip:
Forwarding: 2
491672 total packets received
0 forwarded
0 incoming packets discarded
485413 incoming packets delivered
166022 requests sent out
1 outgoing packets dropped
Icmp:
0 ICMP messages received
0 input ICMP message failed
ICMP input histogram:
8 ICMP messages sent
0 ICMP messages failed
ICMP output histogram:
destination unreachable: 8
IcmpMsg:
OutType3: 8
Tcp:
663 active connection openings
...
3)
Displaying the kernel routing(--route or -r flag) table
[~]
netstat -r
Kernel IP routing table
Destination
Gateway
Genmask
Flags MSS Window irtt Iface
default
_gateway
0.0.0.0
UG 0
0 0 wlan0
10.0.2.0
0.0.0.0
255.255.255.0
U 0
0 0 virbr1
192.168.0.0
0.0.0.0
255.255.255.0
U 0
0 0 wlan0
192.168.122.0
0.0.0.0
255.255.255.0
U 0
0 0 virbr0
4)
Finally, combining different flags
I will run netstat -upv, where
u->UDP internet connections,
p->associated PID/program name,
v->verbose mode
[~]
netstat -upv
(Not all processes could be identified, non-owned process info
will not be shown, you would have to be root to see it all.)
Active Internet connections (w/o servers)
Proto Recv-Q Send-Q Local
Address
Foreign Address
State PID/Program
name
udp
0 0
user:48202
bom07s35-in-f3.1e:https ESTABLISHED 15877/chrome --type
udp
0 0
user:bootpc
_gateway:bootps
ESTABLISHED
-