If the port is not in use, how can bind fail?

If the port is not in use, how can bind fail?

When deploying a webserver on a server today,

Prompt me bind port failed,

I used to use netstat to check whether it was occupied!

 

After sharing the question, awesome colleagues found ip_local_port_range.

This corresponds to the/proc/sys/net/ipv4/ip_local_port_range file.

After opening it, I found that its content is:

1024 65000

 

Then I checked. The two numbers define a port range.

This file specifies the available port range of the so-called "temporary port ".

For example, a program requests a service outside the local machine through a socket,

The requirement of the internal socket is that the dual transmission of communication is an ip address and a port,

During the request, only the ip address and port to be requested are specified, and the local ip address and port are not specified,

In this case, a temporary port is automatically allocated according to the Linux policy.

The valid range of this temporary port is ip_local_port_range.

 

Ip_local_port_range also has a hidden attribute, which is the port in the temporary port range and cannot be bind.

That's why I first encountered the problem.

 

When I want to edit this file to modify the range, the file cannot be saved after modification.

Then I searched for it and said that it would be permanently modified. You can:

Vim/etc/sysctl. conf

Modify net. ipv4.ip _ local_port_range.

Save and run sysctl-p to make it take effect.

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