Generate a SSH key Pair (Public and Private) in Linux

An SSH key pair can be generated by running the ssh-keygen command:

$ ssh-keygen
Generating public/private rsa key pair.
Enter passphrase (empty for no passphrase): 
Enter same passphrase again: 
Your identification has been saved in /home/username/.ssh/id_rsa.
Your public key has been saved in /home/username/.ssh/id_rsa.pub.
The key fingerprint is:
0a:a8:35:2b:66:10:b9:16:4d:b4:45:c7:fa:fa:c8:1e username@localhost
The key's randomart image is:
+--[ RSA 2048]----+
|  .o.o..         |
| .o o ..         |
|o. o  .          |
| o.. .           |
|o.+ . . S        |
|oo o . o         |
|oo.  Eo          |
|o.  ..o          |
|    .+..         |
+-----------------+

This will create two files in your .ssh folder: id_rsa that is the private key (keep it private and treat it like a password) and id_rsa.pub that will contain your public key (that is, the key that you will install in the servers that you want to access).