Friday, February 25, 2011

Tech Notes:- SSH Login Without Password

There are certain circumstances which demand login to mutiple linux servers/desktops without a password. One such situation is to initiate a remote shutdown script to shutdown all servers/desktops in a network. So how do you do it.Here is how it is

Create public key and private key using ssh-key-gen on local machine

sudeep@local-host$ ssh-keygen
Generating public/private rsa key pair.
Enter file in which to save the key (/home/sudeep/.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/sudeep/.ssh/id_rsa.
Your public key has been saved in /home/sudeep/.ssh/
The key fingerprint is:
22:b3:42:cf:a5:b5:28:11:21:c5:be:26:2c:f3:3b:f9 sudeep@local-host

Copy the created public key to remote host using ssh-copy-id

sudeep@local-host$ ssh-copy-id -i ~/.ssh/ remote-host
sudeep@remote-host's password:

ssh-copy-id appends the keys to the remote-host's .ssh/authorized_key

Now try login to the remote host without password

sudeep@local-host$ ssh remote-host
Last login: Thu Feb 24 21:58:45 2008 from
[Note: SSH should not ask for password here.]

sudeep@remote-host$ [Note: You should be on remote-host here]

Using ssh-copy-id along with the ssh-add/ssh-agent

If you have loaded keys to the ssh-agent using the ssh-add, then ssh-copy-id will get the keys from the ssh-agent to copy to the remote-host. That is it copies the keys provided by ssh-add -L command to the remote-host, when you don’t pass option -i to the ssh-copy-id.

sudeep@local-host$ ssh-agent $SHELL
sudeep@local-host$ ssh-add -L
The agent has no identities.

sudeep@local-host$ ssh-add
Identity added: /home/sudeep/.ssh/id_rsa (/home/sudeep/.ssh/id_rsa)

sudeep@local-host$ ssh-add -L
ssh-rsa BBBBA2NzaB2cc1AAAAACIAAAAREcsJLFILxfcR2ASxcA328c62vf72DxbVA
a2rcPHTypq3kIeMUszAPnsxsepe12c/Ow== /home/sudeep/.ssh/id_rsa
Justify Full
sudeep@local-host$ ssh-copy-id -i remote-host
sudeep@remote-host's password:

Now try logging into the machine, with "ssh 'remote-host'", and check in:

to make sure we haven't added extra keys that you weren't expecting.
[Note: This has added the key displayed by ssh-add -L]

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