Linux: How to kill a process using its listening port or used files!

To kill a Linux process you need to know either its PID or the process name, but there is also another way not so well known but still very effective: to kill a process using its listening port or a used file! lets see how we can do this!

I guess most people do the same like me, search for the PID using ps aux and grep

$ ps aux  | grep -i nginx 
root      332640  0.0  0.0  55208 12012 ?        S    16:52   0:00 nginx: master process /usr/sbin/nginx -g daemon on; master_process on; 
www-data  332642  0.0  0.0  55844  5524 ?        S    16:52   0:00 nginx: worker process 
www-data  332643  0.0  0.0  55844  5524 ?        S    16:52   0:00 nginx: worker process 
www-data  332644  0.0  0.0  55844  5524 ?        S    16:52   0:00 nginx: worker process 
www-data  332645  0.0  0.0  55844  5524 ?        S    16:52   0:00 nginx: worker process 
www-data  332646  0.0  0.0  55844  5524 ?        S    16:52   0:00 nginx: worker process 
www-data  332647  0.0  0.0  55844  5524 ?        S    16:52   0:00 nginx: worker process 
www-data  332648  0.0  0.0  55844  5524 ?        S    16:52   0:00 nginx: worker process 
www-data  332649  0.0  0.0  55844  5524 ?        S    16:52   0:00 nginx: worker process

and then kill the process

$ sudo kill -9 332640

But this requires two steps, to find the process and then kill it! using the fuser command this can be consolidated to a single command by passing only the listening port!

The following command sends a kill signal to the PID listening to port 80, which in this case is nginx

$ sudo fuser -k 80/tcp 
80/tcp: 337277 337278 337279 337280 337281 337282 337283 337284 337285

Using this command we killed nginx, lets see know how we can do the same using a file that we know that is open by a process

$ sudo fuser -a -k /var/log/nginx/access.log  
/var/log/nginx/access.log: 346098 346099 346100 346101 346102 346103 346104 346105 346106

The above command killed all processes that currently where using the access.log of nginx.

Note: if you have two different processes working on a file for example nginx and vim will kill both!

Conclusion

The fuser command can be used to identify which processes are using a particular file, directory, or socket. It can also be used to terminate those processes. It is a powerful tool that can be used to troubleshoot problems related to file, directory, or socket usage.