What is the netstat command? How to use netstat command?

The netstatcommand is used to display various network-related information, such as network connections, routing tables, interface status (Interface Statistics), masquerade connections, and multicast memberships (Multicast Memberships) Wait

1 Commonly used options:

-a: (all) displays all options, and does not display LISTEN related ones by default

-t: (tcp) Only display tcp related options

-u: (udp) Only display udp related options

-n: Display IP and port in numbers, can display all numbers Convert to numbers.

-l: List only the service status in Listen (monitoring)

-p: Display the name of the program that establishes the relevant link

-r: Display routing information, Routing table

-e: Display extended information, such as uid, etc.

-s: Statistics based on each protocol

-c: Execute the netstat at regular intervals Order.

-w: raw socket related

2 -tan displays all tcp ports

[root@centos7 ~]# netstat -ant

Active Internet connections (servers and established)

Proto Recv-Q Send-Q Local Address Foreign Address State

tcp 0 0 0.0.0.0:111 0.0.0.0:* LISTEN

tcp 0 0 192.168.122.1:53 0.0.0.0:* LISTEN

tcp 0 0 0.0.0.0:22 0.0.0.0:* LISTEN

tcp 0 0 127.0.0.1:631 0.0.0.0:* LISTEN

tcp 0 0 127.0.0.1:25 0.0.0.0:* LISTEN

tcp 0 52 192.168.29.3:22 192.168.29.1:51029 ESTABLISHED

TCP 0 0 192.168.29.3:22 192.168.29.1:51180 Established

##tcp6 0 0 :::22 :::* LISTEN

tcp6 0 0 ::1:631 :::* LISTEN

tcp6 0 0 ::1:25 :::*

3 show all udp ports -uan

##[root@centos7 ~]# netstat -anu

Active Internet connections (servers and established)Proto Recv-Q Send-Q Local Address Foreign Address State

udp 0 0 0.0.0.0:5353 0.0.0.0 :*

udp 0 0 0.0.0.0:47414 0.0.0.0:*

udp 0 0 192.168.122.1:53 0.0.0.0:*

udp 0 0 0.0 .0.0:67 0.0.0.0:*

4 Display all listening tcp ports -tnl

##[root@centos7 ~]# netstat -tnl

Active Internet connections (only servers)

Proto Recv-Q Send-Q Local Address Foreign Address State

tcp 0 0 0.0 .0.0:111 0.0.0.0:* LISTEN

tcp 0 0 192.168.122.1:53 0.0.0.0:* LISTEN

tcp 0 0 0.0.0.0:22 0.0.0.0:* LISTEN

tcp 0 0 127.0.0.1:631 0.0.0.0:* LISTEN

tcp 0 0 127.0.0.1:25 0.0.0.0:* LISTEN

tcp6 0 0 : ::111 :::* LISTEN

tcp6 0 0 :::22 :::* LISTEN

tcp6 0 0 ::1:631 :::* LISTEN

tcp6 0 0 ::1:25 :::* LISTEN

5 Display all listening udp ports-unl

[root@centos7 ~]# netstat -unl

Active Internet connections (only servers)

Proto Recv-Q Send-Q Local Address Foreign Address State

udp 0 0 0.0.0.0:5353 0.0.0.0:*

udp 0 0 0.0.0.0:47414 0.0.0.0:*

udp 0 0 0.0.0.0:20815 0.0. 0.0:*

udp 0 0 192.168.122.1:53 0.0.0.0:*

udp 0 0 0.0.0.0:67 0.0.0.0:*

udp 0 0 0.0.0.0:68 0.0.0.0:*

udp 0 0 0.0.0.0:68 0.0.0.0:*

udp 0 0 0.0.0.0:9804 0.0.0.0:*

udp6 0 0 :::12799 :::*

udp6 0 0 :::37953 :::*

6 show routing table –rn

[root@centos7 ~]# netstat -nr

Kernel IP routing table

Destination Gateway Genmask Flags MSS Window irtt Iface

0.0.0.0 192.168.29.1 0.0.0.0 UG 0 0 0 ens33

192.168.29.0 0.0.0.0 255.255.255.0 U 0 0 0 ens33

192.168. 122.0 0.0.0.0 255.255.255.0 U 0 0 0 virbr0

[root@centos7 ~]# route -n

Kernel IP routing table

Destination Gateway Genmask Flags Metric Ref Use Iface

0.0.0.0 192.168.29.1 0.0.0.0 UG 100 0 0 ens33

192.168.29.0 0.0.0.0 255.255.255.0 U 100 0 0 ens33

192.168. 122.0 0.0.0.0 255.255.255.0 U 0 0 0 virbr0

7 Display statistics for each protocol

(1) Display all ports Statistics netstat -s[root@centos7 ~]# netstat -s

Ip:

3808 total packets received

0 forwarded

0 incoming packets discarded

2444 incoming packets delivered

2254 requests sent out

32 outgoing packets dropped

Icmp:

676 ICMP messages received

0 input ICMP message failed.

ICMP input histogram:

destination unreachable: 148

echo replies: 528

717 ICMP messages sent

0 ICMP messages failed

ICMP output histogram:

destination unreachable: 148

echo request: 569

[……]

（2）显示 TCP 端口的统计信息 netstat -st

[root@centos7 ~]# netstat -st

IcmpMsg:

InType0: 528

InType3: 148

OutType3: 148

OutType8: 569

Tcp:

0 active connections openings

2 passive connection openings

0 failed connection attempts

0 connection resets received

2 connections established

1637 segments received

1418 segments send out

0 segments retransmited

0 bad segments received.

0 resets sent

（3）显示 UDP 端口的统计信息 netstat -su

[root@centos7 ~]# netstat -su

IcmpMsg:

InType0: 528

InType3: 148

OutType3: 148

OutType8: 569

Udp:

0 packets received

140 packets to unknown port received.

0 packet receive errors

169 packets sent

0 receive buffer errors

0 send buffer errors

UdpLite:

IpExt:

InMcastPkts: 27

OutMcastPkts: 33

InBcastPkts: 766

InOctets: 410294

OutOctets: 432666

InMcastOctets: 4963

OutMcastOctets: 5444

InBcastOctets: 179503

InNoECTPkts: 3848

8 显示 PID 和进程名称 netstat -p

[root@centos7 ~]# netstat -p

Active Internet connections (w/o servers)

Proto Recv-Q Send-Q Local Address Foreign Address State PID/Program name

tcp 0 52 centos7.3.local:ssh gateway:51029 ESTABLISHED 1552/sshd: root@pts

tcp 0 0 centos7.3.local:ssh gateway:51180 ESTABLISHED 1854/sshd: root@pts

Active UNIX domain sockets (w/o servers)

Proto RefCnt Flags Type State I-Node PID/Program name Path

unix 2 [ ] DGRAM 8520 1/systemd /run/systemd/notify

unix 2 [ ] DGRAM 8522 1/systemd /run/systemd/cgroups-agent

unix 5 [ ] DGRAM 8542 1/systemd /run/systemd/journal/socket

unix 28 [ ] DGRAM 8544 1/systemd /dev/log

unix 2 [ ] DGRAM 11419 1/systemd /run/systemd/shutdownd

unix 3 [ ] STREAM CONNECTED 23993 1276/ibus-x11

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