List of recipes to debug or just do what you need on MAC or LINUX machine.

Find the pid of a listening process + kill it

I found this Stackoverflow question.

On MAC

lsof -i tcp:8018

display a table like that

COMMAND  PID   USER   FD   TYPE             DEVICE SIZE/OFF NODE NAME
node    2091 slucas   21u  IPv4 0x55f00507a74a3aa5      0t0  TCP *:4506 (LISTEN)

To kill the process

kill -9   2091

ssh add ssh keys to authorized keys in a server

cat ~/.ssh/id_rsa.pub | ssh root@your.ip.address "cat >> ~/.ssh/authorized_keys"

authorized_keys is file that list all authorized keys in the remote server.

for root login check that PermitRootLogin without-password is set in you sshdConfig file

​https://www.digitalocean.com/community/tutorials/how-to-use-ssh-keys-with-digitalocean-droplets​