Add new pem file to EC2 - ssh - key - generate

get_public_key.sh

Connect to machine you want to give access
$ sudo adduser <onur.demir>
$ sudo su <onur.demir>

make sure your are in user's home directory.
$ cd
Create .ssh directory, and change the directory permission to 700 (only the file owner can read, write or open the directory):
$ mkdir .ssh
$ chmod 700 .ssh
Create an empty file called authorized_keys in the .ssh directory and change its permissions to 600 (only the file owner can read or write to the file)
$ touch authorized_keys
$ chmod 600 authorized_keys

Go to AWS EC2 console. In the left navigation pane, select "Key Pairs". Then click "Create Key Pair". 

Download private pem file. 

Run below command in any linux or mac machine in order to get the public key of the private key:

ssh-keygen -y -f <pem-file>

Again in the machine you want to give access, open .ssh/authorized_key and append the public key just below the existing one(no empty line).
Add the name of the private key also like below:
ssh-rsa dfasgwfsdfefwefsdadqwDAQABAAABAQCl6BhEWO0Mzm2dasgtwfdsfwdqdq keyname

than connect to EC2 with your new user like:
$ ssh -i <pem-file> <new-username>@<ip>

your done :)