SHELL

add existing key to ssh

cp /path/to/my/key/id_rsa ~/.ssh/id_rsa
cp /path/to/my/key/id_rsa.pub ~/.ssh/id_rsa.pub
# change permissions on file
sudo chmod 600 ~/.ssh/id_rsa
sudo chmod 600 ~/.ssh/id_rsa.pub
# start the ssh-agent in the background
eval $(ssh-agent -s)
# make ssh agent to actually use copied key
ssh-add ~/.ssh/id_rsa

add key file to ssh

sudo chmod 400 [key file]
sudo ssh -i [key file] [username]@[ip]

ssh add new key

$ eval "$(ssh-agent -s)"
> Agent pid 59566