How to use port 80 in Tomcat under Linux system

Application Scenario

In many cases, we install software such as tomcat or nginx on the Linux server.

When we want to use port 80, we will get an error if we don't start it as root user.

This is because, for Linux systems, ports below 1024 are not available to ordinary users.

There are two solutions to this problem on the Internet. One is to give the file root permissions.

Another method is to do port jump. I think port jump may be safer. I will focus on how to configure it.

IPTABLES

Here we mainly do port forwarding on this machine. I will mainly talk about how to set and delete it.

For more information about iptables, you can refer to a lot of information on the Internet.

Add a port mapping

Now we have to do one thing, assuming that we have tomcat installed on our Linux. The default access port is 8080.

Now I want to be able to access tomcat when the user accesses port 80.

Just execute the command under the root user

iptables -t nat -A PREROUTING -p tcp –dport 80 -j REDIRECT –to-port 8080 

-t nat : Indicates which table I want to operate on. (If not specified, it means filter. The default is filter)

-A PREROUTING: A means adding. It means I want to add a rule in PREROUTING

--dport 80 : If requesting port 80.

--to-port 8080 : Then go to port 8080.

The test is as follows:

How to Delete a Rule

From the above we can see that we added the rule in PREROUTING of the nat table.

So we need to delete this rule in PREROUTING of the nat table.

iptables -t nat -L -nv --line-numbers

The purpose of this command is to list the rules in the nat table and give a num.

Then we can use this id to delete the rule.

If you don't write -t ​​nat, the default search is the filter table. Then the rules cannot be found.

This statement can be used to delete the rule.

-t nat : means I want to operate this table. If not specified, it means filter.

-D: indicates to perform a delete operation

PREROUTING: Indicates which chain in the NAT table. The number 1 behind it is the num in the above figure.

Summarize

I did the following experiments, nginx occupies port 80 and tomcat occupies port 8080.

Open nginx, tomcat

1. If redirection is enabled, nginx cannot be accessed because when accessing port 80, it jumps to port 8080.

2 Close port forwarding and you can access nginx.

3 From the above, we can see that port forwarding will not occupy the port.

4 If adding rule access does not achieve the desired effect, clear the browser cache.

5 All the above operations will disappear after restart. If you want to keep the operations, please execute service iptables restart

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