Ubuntu – How to set up password-less SSH login

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I want to be able to login to a remote via ssh without having to enter the password all the time.

How do I set it up?
Is a different command required to execute a password-less session?

Best Answer

Answer

Execute this commands:

ssh-keygen

Then you'll need to copy the new key to your server:

ssh-copy-id user@host
## or if your server uses custom port no:
ssh-copy-id "user@host -p 1234"

After the key is copied, ssh into the machine as normal:

ssh user@host

You can now login without entering a password from the particular machine you executed the commands at.

Example

not-marco@rinzwind-desktop:~$ ssh-keygen 
Generating public/private rsa key pair.
Enter file in which to save the key (/home/not-marco/.ssh/id_rsa): 
Created directory '/home/not-marco/.ssh'.
Enter passphrase (empty for no passphrase): 
Enter same passphrase again: 
Your identification has been saved in /home/not-marco/.ssh/id_rsa.
Your public key has been saved in /home/not-marco/.ssh/id_rsa.pub.
The key fingerprint is:
b1:25:04:21:1a:38:73:38:3c:e9:e4:5b:81:e9:ac:0f not-marco@rinzwind-desktop
The key's randomart image is:
+--[ RSA 2048]----+
|.o= . oo.        |
|*B.+ . .         |
|*=o .   o .      |
| = .     =       |
|. o     S        |
|E.               |
| o               |
|  .              |
|                 |
+-----------------+

not-marco@rinzwind-desktop:~$ ssh-copy-id not-marco@server
not-marco@server's password: 
Now try logging into the machine, with "ssh 'not-marco@server'", and check in:

  ~/.ssh/authorized_keys

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

Explanation

This assumes you already can successfully connect to your server via SSH.

You'll need to generate an SSH Keypair which will allow you to identify you as yourself without using a password. You can opt to protect keys with a passcode if you wish, but this can be left blank allowing totally password-less SSH access.

First create your SSH Keypair by running ssh-keygen this will create an id_rsa and id_rsa.pub file. The pub file is what goes on the servers, the private key (id_rsa) is what stays with you and is how you identify yourself.
Next copy the public key to your server with ssh-copy-id user@server replacing user with your remote user and server with the machine DNS name or IP address. It'll prompt for your SSH password, enter it and if all completes successfully you'll be able to access the machine via ssh user@server without needing a password.

References

https://help.ubuntu.com/community/SSH/OpenSSH/Keys

Related Solutions

Ubuntu – how to turn off password-less login for ssh

Disable pubkey authentication on the client where you don't want to use it.

ssh -o PubkeyAuthentication=no your_host

or in your ~/.ssh/config:

Host your_host
  PubkeyAuthentication no

If you want to remove the public key from the server, you need to remove the appropriate line from ~/.ssh/authorized_keys on server.

Ubuntu – How to set password-less ssh login for multiple remote severs

Why my public key can't be saved as /root/.ssh/myvps.pub?

Your keys can be saved with any name you'd like. However, the ssh client will only automatically search for a few standard names, id_rsa, id_dsa, id_ecdsa, or id_ed25519. If you want to save it under any other name, you need to specify the file name either on the command line:

ssh -i ~/.ssh/myvps root@vps_ip2

or in your ~/.ssh/config file:

Host vps_ip2
    IdentityFile ~/.ssh/myvps
    User root