How to know what program is listening on a given port?

I face this issue alot where I need to know list of occupied ports and the pids, I keep forgetting the commands so I thought about posting them here for future references and for anyone who needs it :
 
I use this command to have a full detail :

sudo netstat -taupen

if I need to know exactly which one is listening on specific port (i.e. 8080) I use this :

sudo netstat -tapen | grep ":8080"

P.S: the above commands for ubuntu OS, I have not tried them on over distributions

 

Recover unreachable EC2 CentOS instance

So .. I was working for three days setting up a CentOS ec2 instance environment, and I was using root credentials to login into the VM. 

I decided to stop using password and start using SSH Keys since I am going to share the VM with other developers. So I setup the ssh authorized keys properly and dropped the root password but I forgot to tweak ssh configuration to permite Empty Passwords! and I got stuck outside the VM with password prompt that does not accept any single damn word! :)

So, the simplest solution I found on the internet was to mount the volume to another ec2 instance, fix the password settings and put it back to the unreachable ec2 instance.

Here are the steps :

• First you need to setup Amazon ec2 API tool
• Get instance id from ec2
• Get volume id from ec2
• Stop the unreachable instance
• Detach the volume from unreachable instance
• Start the debugger instance
• attach the volume to the debugger instance
• ssh the debugger instance
• mount the volume
• fix the ssh setting to enable/permits empty passwords
• unmount the volume
• detatch the volume from the debugger instance
• attach the volume to the unreachable instance
• now try to ssh, if it did not work you need to repeat the steps and keep fixing the configs until it works.

 I will try to edit this post to provide more details soon. But for now, hope this helps you to fix your problem, you can leave a comment if you need any help!