Netstat command, understand it in one article
Preface
In backend development, the netstat command can never be bypassed. Not only is it often used at work, but it is also tested frequently in interviews. The netstat command has many corresponding options and is relatively powerful. Netstat is commonly used to view the status of background service processes.
netstat can be used to print statistics on network connections, routing tables, and connections. Let’s learn about it below.
Print all connections
Use -a to list all connections.
[root@VM-16-9-centos ~]# netstat -a
Active Internet connections (servers and established)
Proto Recv-Q Send-Q Local Address Foreign Address State
tcp 0 0 0.0.0.0:ssh 0.0.0.0:* LISTEN
tcp 0 0 VM-16-9-centos:49326 169.254.0.55:lsi-bobcat ESTABLISHED
tcp 0 52 VM-16-9-centos:ssh 119.137.1.7:20029 ESTABLISHED
tcp 0 0 VM-16-9-centos:ssh 113.110.224.255:63626 ESTABLISHED
tcp6 0 0 [::]:mysql [::]:* LISTEN
udp 0 0 0.0.0.0:bootpc 0.0.0.0:*
udp 0 0 VM-16-9-centos:ntp 0.0.0.0:*
udp 0 0 VM-16-9-centos:ntp 0.0.0.0:*
udp 0 0 0.0.0.0:38064 0.0.0.0:*
udp6 0 0 VM-16-9-centos:ntp [::]:*
udp6 0 0 VM-16-9-centos:ntp [::]:*
Print TCP or UDP connection
Use the -t option to list connections for the TCP protocol.
[root@VM-16-9-centos ~]# netstat -t
Active Internet connections (w/o servers)
Proto Recv-Q Send-Q Local Address Foreign Address State
tcp 0 0 VM-16-9-centos:49326 169.254.0.55:lsi-bobcat ESTABLISHED
tcp 0 52 VM-16-9-centos:ssh 119.137.1.7:20029 ESTABLISHED
tcp 0 0 VM-16-9-centos:ssh 113.110.224.255:63626 ESTABLISHED
tcp 0 0 VM-16-9-centos:ssh vps-d395feee.vps.:39128 ESTABLISHED
Use the -u option to list connections for the UDP protocol.
[root@VM-16-9-centos ~]# netstat -u
Active Internet connections (w/o servers)
Proto Recv-Q Send-Q Local Address Foreign Address State
Disable reverse domain name resolution
Use the -n option to disable domain name resolution, which can speed up lookups.
[root@VM-16-9-centos ~]# netstat -n
Active Internet connections (w/o servers)
Proto Recv-Q Send-Q Local Address Foreign Address State
tcp 0 0 172.17.16.9:49326 169.254.0.55:5574 ESTABLISHED
tcp 0 52 172.17.16.9:22 119.137.1.7:20029 ESTABLISHED
tcp 0 0 172.17.16.9:22 113.110.224.255:63626 ESTABLISHED
tcp 0 0 172.17.16.9:52236 169.254.0.4:80 TIME_WAIT
Display the corresponding program identification code and program name
Use the -p option to list listening sockets.
[root@VM-16-9-centos ~]# netstat -p
Active Internet connections (w/o servers)
Proto Recv-Q Send-Q Local Address Foreign Address State PID/Program name
tcp 0 0 VM-16-9-centos:49326 169.254.0.55:lsi-bobcat ESTABLISHED 1400/YDService
tcp 0 52 VM-16-9-centos:ssh 119.137.1.7:20029 ESTABLISHED 22131/sshd: root@pt
tcp 0 0 VM-16-9-centos:ssh host-188-14-121-2:55529 TIME_WAIT -
tcp 0 0 VM-16-9-centos:ssh 113.110.224.255:63626 ESTABLISHED 32201/sshd: root@pt
Print listening connections
Use the -l option to list listening sockets.
[root@VM-16-9-centos ~]# netstat -l
Active Internet connections (only servers)
Proto Recv-Q Send-Q Local Address Foreign Address State
tcp 0 0 0.0.0.0:ssh 0.0.0.0:* LISTEN
tcp6 0 0 [::]:mysql [::]:* LISTEN
udp 0 0 0.0.0.0:bootpc 0.0.0.0:*
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Print connection process information
Use the -p option to view process information.
[root@VM-16-9-centos ~]# netstat -p
Active Internet connections (w/o servers)
Proto Recv-Q Send-Q Local Address Foreign Address State PID/Program name
tcp 0 0 VM-16-9-centos:49326 169.254.0.55:lsi-bobcat ESTABLISHED 1400/YDService
tcp 0 0 VM-16-9-centos:48680 169.254.0.55:webcache TIME_WAIT -
tcp 0 52 VM-16-9-centos:ssh 119.137.1.7:20029 ESTABLISHED 22131/sshd: root@pt
tcp 0 0 VM-16-9-centos:ssh 113.110.224.255:63626 ESTABLISHED 32201/sshd: root@pt
tcp 0 0 VM-16-9-centos:ssh host-188-14-121-2:56025 ESTABLISHED 10384/sshd: unknown
Print network work information statistics table
Use the -s option to view process information (only partial results are displayed).
[root@VM-16-9-centos ~]# netstat -s
Ip:
7502855 total packets received
0 forwarded
0 incoming packets discarded
7502837 incoming packets delivered
7624338 requests sent out
40 dropped because of missing route
Icmp:
938052 ICMP messages received
147 input ICMP message failed.
ICMP input histogram:
destination unreachable: 411
timeout in transit: 8
redirects: 2
echo requests: 937623
echo replies: 7
timestamp request: 1
946258 ICMP messages sent
0 ICMP messages failed
ICMP output histogram:
destination unreachable: 8634
echo replies: 937623
timestamp replies: 1
Print network interface
Use the -i option to view process information.
[root@VM-16-9-centos ~]# netstat -i
Kernel Interface table
Iface MTU RX-OK RX-ERR RX-DRP RX-OVR TX-OK TX-ERR TX-DRP TX-OVR Flg
eth0 1500 7825094 0 0 0 7712988 0 0 0 BMRU
lo 65536 10230 0 0 0 10230 0 0 0 LRU
Continuously output information
Use the -c option to view process information.
[root@VM-16-9-centos ~]# netstat -c
Active Internet connections (w/o servers)
Proto Recv-Q Send-Q Local Address Foreign Address State
tcp 0 0 VM-16-9-centos:49326 169.254.0.55:lsi-bobcat ESTABLISHED
tcp 0 52 VM-16-9-centos:ssh 119.137.1.7:20029 ESTABLISHED
tcp 0 0 VM-16-9-centos:ssh vps-d395feee.vps.:39442 ESTABLISHED
tcp 0 0 VM-16-9-centos:ssh 113.110.224.255:63626 ESTABLISHED
tcp 0 0 VM-16-9-centos:52660 169.254.0.4:http TIME_WAIT
tcp 0 0 VM-16-9-centos:ssh b3d278e1.virtua.c:35113 TIME_WAIT
tcp 0 0 VM-16-9-centos:ssh 58.230.147.230:56693 TIME_WAIT
Active UNIX domain sockets (w/o servers)
Proto RefCnt Flags Type State I-Node Path
unix 3 [ ] DGRAM 7444 /run/systemd/notify
Check the port based on the process pid
Use the grep command to find out the listening port through the process pid.
[root@VM-16-9-centos test]# netstat -nap|grep 12178
tcp6 0 0 :::8888 :::* LISTEN 12178/gin
Check process based on port
Use the grep command to find out the process pid through the listening port .
[root@VM-16-9-centos test]# netstat -nap|grep 8888
tcp6 0 0 :::8888 :::* LISTEN 12178/gin
Statistics network socket status
Use the awk command to count the number corresponding to the socket status.
[test]# netstat -n | awk '/^tcp/ {++S[$NF]} END {for(a in S) print a, S[a]}'
ESTABLISHED 5
TIME_WAIT 2
babble
The netstat command is not difficult, but it has many options and is commonly used in work, so be sure to master it. This article can be used as a reference manual for everyone's netstat.
end
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