Linux forced release of occupied ports and Linux firewall port opening method detailed explanation

When installing nginx, mysql, tomcat and other services, we may encounter the problem that the ports we need to use are inexplicably occupied. Here is how to solve this problem.

Speaking of ports, we have to mention firewalls. This article will also briefly introduce how to configure firewall development ports.

Various methods to view port status in Linux

The mapping relationship of all ports is in the /etc/services file.

A brief introduction to Linux ports. Port numbers range from 0 to 65536. The uses of each numbered port are as follows:

0-1023: Well-known ports, bound to common services (FTP, SSH)

1024-49151: registered port, used to bind to some services

49152-65535: Dynamic or private ports, can be used for any network connection

Ports are divided into TCP and UDP transmission protocols.

Linux view port status command

You can use the following command to check the port status. Click the command to adjust the usage details of each command:

nmap command, port scanning use

netstat detects the development port

lsof checks port descriptors

# View the port bound to this machine nmap 127.0.0.1

# Check port 3306 netstat -anlp | grep 3306

# Check interface 3306 lsof -i:3306

How to release occupied ports in Linux

The solution steps are as follows:

Find the process occupying the port

Kill the process

Use the following command:

# Can be written as a command

netstat -anp|grep 8080|awk '{print $7}'|awk -F '/' '{print $1}'|xargs kill -s 9

The meaning of each command is as follows:

netstat -anp displays all network usage and shows the programs using it

grep 8080 matches the records of port 8080 (may include 18080)

awk '{print $7}' outputs the process in the 7th column in the following format: 18989/nginx

awk -F '/' '{print $1}' intercepts the process PID: 18989

xargs kill -s 9 uses the output of the previous command as a parameter to kill the process

Step-by-step solution to release occupied ports

Check whether the port is occupied

For example, if you need to check whether port 8080 is occupied, you can use the following command

netstat -an | grep 8080

Query the process occupying the port

You can use the lsof command to view

lsof -i:8080

You can also use netstat and grep to view

netstat -anp|grep 8080

The last line of the command is the PID and name of the process occupying port 8080.

Kill the process occupying the port

You can use the kill command to directly kill the process found in the previous step.

kill -9 19664

Linux firewall releases ports

Linux firewall startup and shutdown

The firewall introduced below is iptable, which is not applicable to firewalld.

Turn on the firewall (permanent after restart): chkconfig iptables on
Turn off the firewall (permanent after reboot): chkconfig iptables off
Enable the firewall (effective immediately and invalid after reboot): service iptables start
Disable the firewall (immediately effective, invalid after reboot): service iptables stop
Restart the firewall: service iptables restart

Check the firewall status in Linux

You can use the following command to view:

/etc/init.d/iptables status

# Or simply iptables status
iptables -L

# You can also directly view the configuration file vim /etc/sysconfig/iptables 

Open a port in Linux firewall

For example, to open port 8080, use the following command:

iptables -A INPUT -p tcp --dport 8080 -j ACCEPT
# You also need to restart the service service iptables restart

# You can also directly edit the configuration file vim /etc/sysconfig/iptables
# Then add a line to the end of the file to open all ports between 8080 and 8181 iptables -A INPUT -p tcp --dport 8080:8181 -j ACCEPT

in

The –A parameter is considered to add a rule
–p specifies the protocol, we usually use TCP protocol, of course there is also UDP
–dport is the target port. When data enters the server from the outside, it is the target port.
–sport data goes out from the server, so it is used as the data source port
–j specifies ACCEPT - receive or DROP not receive

The above is about Linux forced release of occupied ports and Linux firewall port opening method. For more articles about Linux ports, please click the related articles below