Generating SSH public/private key pair (Linux / Ubuntu)

Now that in previous post, we have seen how to generate SSH Public / Private keypair in Windows system, how about generating it in Linux or Ubuntu ?   Well, here it is.

To generate SSH public/private key pair :

Step 1 : Open a shell or command-line instance on your computer.

Step 2 : Ensure that you don't already have a public key saved to your computer. To do this, run the following command:

$ cd ~/. ssh (# Change into your . ssh folder)
$ ls -l (# Lists the files in your . ssh directory, if they exist)

{ensure you have 700 permission to . ssh i.e. command : $ sudo chmod 700 . ssh }

If the directory and key file (id_rsa. pub) exists, run the following commands to back up the key id_rsa, as this procedure overwrites your current key if it is named id_rsa.

$ mkdir key_backup
$ mv id_rsa* key_backup

Step 3 : Generate a new public/private key pair using the keygen command:

$ ssh-keygen -b 4096

The keygen command prompts you for the directory to contain the key.

Generating public/private rsa key pair. 
Enter file in which to save the key (/home/[user_dir]/. ssh/id_rsa): 
Press Enter to accept the default location of /. ssh/id_rsa in your user directory. 
Enter passphrase (empty for no passphrase): [passphrase] 
Enter same passphrase again: [passphrase] 

Substitute [passphrase] with your own text. This is for encrypting the private key on your computer. It's possible to use a blank [passphrase],But if you do this, another user can impersonate you with a copy of the key file. 

Note: Be sure to keep track of the [passphrase] since you will need to enter it when using the key.​

The keygen command displays the following output:

Generating public/private rsa key pair. 
Your identification has been saved in /home/[user_dir]/. ssh/id_rsa. 
Your public key has been saved in /home/[user_dir]/. ssh/id_rsa.pub. 
The key fingerprint is: 
52:96:e9:c8:06:c2:57:26:6d:ef:2f:0c:d9:81:f4:1c username@hostname 
{ensure you have 600 permission to id_rsa i.e. command : sudo chmod 600 id_rsa }

Step 4 : In Ubuntu(or any Linux distri. with Xwindows), a similar tool is xclip. I like to make this alias:

alias pbcopy='xclip -selection clipboard'
alias pbpaste='xclip -selection clipboard -o'

If you do not have "xclip" :

sudo apt-get install xclip -y

And Then follow the above steps of aliasing..

Step 5 : Copy the key to your clipboard. Run the following code to copy the key to your clipboard:

pbcopy < ~/. ssh/id_rsa. pub
# Copies the contents of the id_rsa. pub file to your clipboard

 There !! You're all set for using these newly created public / private keypair.

Reference : https://help.github.com/articles/generating-ssh-keys/#platform-linux