SHH_remoteExecute_setup~

//## Do this in the local computer, mean AWS EC2 in this case
//## the server (the computer you want to ssh to hold public key), your local computer holds private key
// https://help.ubuntu.com/community/SSH/OpenSSH/Configuring
// sudo apt-get install openssh-server // EC2 ubuntu came
sudo cp /etc/ssh/sshd_config /etc/ssh/sshd_config.factory-defaults // make a copy of original config file
sudo chmod a-w /etc/ssh/sshd_config.factory-defaults // protect it

// disable password authentication
sudo gedit /etc/ssh/sshd_config
	#PasswordAuthentication yes -> PasswordAuthentication no
	UsePAM no
sudo /etc/init.d/ssh reload
// I didn't do this two in EC2, but I did this in my own computer (which is the server)
sudo restart ssh
sudo systemctl restart ssh

// generate RSA keys
mkdir ~/.ssh
chmod 700 ~/.ssh
chmod 600 authorized_keys
ssh-keygen -t rsa
	passphrase: so that we can learn to pick ourselves up
	(!!! this time: no passphrase)
// then pass the .pub key to the server, you can simply copy and paste it from termial by opening the key:
cat id_rsa.pub

// Important! go to the server, which it my computer, add the key to autorized key
cat id_rsa.pub >> ~/.ssh/authorized_keys

// Find IP in my own computer (the server)
curl -s checkip.dyndns.org | sed -e 's/.*Current IP Address: //' -e 's/<.*$//' 

// connect by: 
ssh oscar@132.236.79.195


//--------------- I accitantly delete the authorized_keys in EC2 -------------
1. stop current instance
2. create a new one
3. detach current EBS volumn
4. attach to the new instance
5. (From AWS) mount EBS volumn in the new instance (http://docs.aws.amazon.com/AWSEC2/latest/UserGuide/ebs-using-volumes.html)
6. In my own computer:
	1. ssh-keygen -y (this command generate public key)
	2. scp the public key to instance
7. cat the public key to authorized_keys
8. umount the volume FIRST!!!
9. detach the volume
10. attach the volume as /dev/sda1 (which is root)
11. restart the old instance

// First try don't work:
copy the authorized_keys from the new instance directly to the old one. (Since I create the new instance by using the same key)

Effectively you've pulled the hard drive out, plugged it into a working system, made some changes and put it back.
Then use the private key on my own computer to duplicate another public key then add to authorized key.