Passwordless ssh login

You can login to a remote Linux server without entering password in 3 simple steps using ssky-keygen and ssh-copy-id as explained in this article.

ssh-keygen creates the public and private keys. ssh-copy-id copies the local-host’s public key to the remote-host’s authorized_keys file. ssh-copy-id also assigns proper permission to the remote-host’s home, ~/.ssh, and ~/.ssh/authorized_keys.

This article also explains 3 minor annoyances of using ssh-copy-id and how to use ssh-copy-id along with ssh-agent.

Step 1: Create public and private keys using ssh-key-gen on local-host

jsmith@local-host$ [Note: You are on local-host here]

jsmith@local-host$ ssh-keygen
Generating public/private rsa key pair.
Enter file in which to save the key (/home/jsmith/.ssh/id_rsa):[Enter key]
Enter passphrase (empty for no passphrase): [Press enter key]
Enter same passphrase again: [Pess enter key]
Your identification has been saved in /home/jsmith/.ssh/id_rsa.
Your public key has been saved in /home/jsmith/.ssh/id_rsa.pub.
The key fingerprint is:
33:b3:fe:af:95:95:18:11:31:d5:de:96:2f:f2:35:f9 jsmith@local-host

Step 2: Copy the public key to remote-host using ssh-copy-id

jsmith@local-host$ ssh-copy-id -i ~/.ssh/id_rsa.pub remote-host
jsmith@remote-host's password:
Now try logging into the machine, with "ssh 'remote-host'", and check in:

.ssh/authorized_keys

to make sure we haven't added extra keys that you weren't expecting.

Note: ssh-copy-id appends the keys to the remote-host’s .ssh/authorized_key.

Step 3: Login to remote-host without entering the password

jsmith@local-host$ ssh remote-host
Last login: Sun Nov 16 17:22:33 2008 from 192.168.1.2
[Note: SSH did not ask for password.]

jsmith@remote-host$ [Note: You are on remote-host here]

The above 3 simple steps should get the job done in most cases.

Note:
Recently I started to get  Agent admitted failure to sign using the key on ubuntu 12.04, but this solved the problem:

# start the ssh-agent in the background
eval "$(ssh-agent -s)

After setting that up refer to "Disable root login" to disable root login for extra security. 

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