Gunicorn Connection in Use: (‘’, 8000)

I develop web services using python flask. One of the common error that I see while deploying the application is “Gunicorn Connection in Use: (‘’, 8000)”.

This means that the port 8000 is busy with some other running process. But when I check the status of the port with the following command, I get empty response. That means there are no active application using the port. Some stale process is making the port busy.

netstat -tulpn | grep 8000

I even tried with the ps command to see any active process, but that also did not help.

ps -aux

If the ps command list the process, we can kill the process directly using the kill command

kill -9 {PID}

In my case I do not have the PID. So the only option to kill these kind of zombie application by using the below command.

sudo fuser -k {PORT}/tcp

In my case, the port number is 8000, so the command will be.

sudo fuser -k 8000/tcp

This trick helped me several times, hope this helps someone else also.


SELinux modes – Simple explanation

Everyone who uses linux might be familiar with SELinux. The full form of SELinux is Security-Enhanced Linux. It is a kernel level security module that enhances the access level security policies.

In this post I will be quickly explaining about the various modes in SELinux.

There are three modes in SELinux

  • Enforcing
  • Permissive
  • Disabled

In CentOS and RHEL systems , the SELinux configurations are controlled using the configuration file /etc/sysconfig/selinux.

The changes made to this file needs a system reboot. We can disable the SELinux permanently only with a system reboot. But we can set the SELinux into permissive mode without reboot. This can be easily performed by issuing a setenforce command. The details are explained in my another blog post.

Here we can set SELinux to any of the modes mentioned above.

In the Enforcing mode, SELinux is completely active and it will allow access only using the SELinux policies. User can configure the policies to enable access to their application.

In the Permissive mode, the SELinux will be monitoring and logging all the activities that would have been denied if it is in the enforcing state. The SELinux will not block any activities in this state.

In the Disabled mode, SELinux will be completely disabled.