SSH Passwordless Login Using SSH Keygen in 5 Easy Steps

SSH (Secure SHELL) is an open-source and most trusted network protocol that is used to login to remote servers for the execution of commands and programs. It is also used to transfer files from one computer to another computer over the network using a secure copy (SCP) Protocol.

In this article, we will show you how to setup password-less login on RHEL/CentOS and Fedora using ssh keys to connect to remote Linux servers without entering a password. Using Password-less login with SSH keys will increase the trust between two Linux servers for easy file synchronization or transfer.

SSH Passwordless Login

My Setup Environment
SSH Client : 192.168.0.12 ( Fedora 21 )
SSH Remote Host : 192.168.0.11 ( CentOS 7 )

If you are dealing with a number of Linux remote servers, then SSH Password-less login is one of the best ways to automate tasks such as automatic backups with scripts, synchronization files using SCP, and remote command execution.

In this example, we will set up SSH password-less automatic login from server 192.168.0.12 as user tecmint to 192.168.0.11 with user sheena.

Step 1: Create Authentication SSH-Keygen Keys on – (192.168.0.12)

First login into server 192.168.0.12 with user tecmint and generate a pair of public keys using the following command.

[tecmint@tecmint.com ~]$ ssh-keygen -t rsa

Generating public/private rsa key pair.
Enter file in which to save the key (/home/tecmint/.ssh/id_rsa): [Press enter key]
Created directory '/home/tecmint/.ssh'.
Enter passphrase (empty for no passphrase): [Press enter key]
Enter same passphrase again: [Press enter key]
Your identification has been saved in /home/tecmint/.ssh/id_rsa.
Your public key has been saved in /home/tecmint/.ssh/id_rsa.pub.
The key fingerprint is:
5f:ad:40:00:8a:d1:9b:99:b3:b0:f8:08:99:c3:ed:d3 [email protected]
The key's randomart image is:
+--[ RSA 2048]----+
|        ..oooE.++|
|         o. o.o  |
|          ..   . |
|         o  . . o|
|        S .  . + |
|       . .    . o|
|      . o o    ..|
|       + +       |
|        +.       |
+-----------------+

Create SSH RSA Key

Step 2: Create .ssh Directory on – 192.168.0.11

Use SSH from server 192.168.0.12 to connect server 192.168.0.11 using sheena as a user and create .ssh directory under it, using the following command.

[tecmint@tecmint ~]$ ssh sheena@192.168.0.11 mkdir -p .ssh

The authenticity of host '192.168.0.11 (192.168.0.11)' can't be established.
RSA key fingerprint is 45:0e:28:11:d6:81:62:16:04:3f:db:38:02:la:22:4e.
Are you sure you want to continue connecting (yes/no)? yes
Warning: Permanently added '192.168.0.11' (ECDSA) to the list of known hosts.
sheena@192.168.0.11's password: [Enter Your Password Here]

Create SSH Directory Under User Home

Step 3: Upload Generated Public Keys to – 192.168.0.11

Use SSH from server 192.168.0.12 and upload a new generated public key (id_rsa.pub) on server 192.168.0.11 under sheena‘s .ssh directory as a file name authorized_keys.

[tecmint@tecmint ~]$ cat .ssh/id_rsa.pub | ssh sheena@192.168.0.11 'cat >> .ssh/authorized_keys'

sheena@192.168.1.2's password: [Enter Your Password Here]

Upload RSA Key

Step 4: Set Permissions on – 192.168.0.11

Due to different SSH versions on servers, we need to set permissions on .ssh directory and authorized_keys file.

[tecmint@tecmint ~]$ ssh sheena@192.168.0.11 "chmod 700 .ssh; chmod 640 .ssh/authorized_keys"

sheena@192.168.0.11's password: [Enter Your Password Here]

Set Permission on SSH Key

Step 5: Login from 192.168.0.12 to 192.168.0.11 Server without Password

From now onwards you can log into 192.168.0.11 as sheena user from server 192.168.0.12 as tecmint user without a password.

[tecmint@tecmint ~]$ ssh sheena@192.168.0.11

SSH Remote Passwordless Login

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262 thoughts on “SSH Passwordless Login Using SSH Keygen in 5 Easy Steps”

  1. It works perfectly for me.

    Allow user agent on local/client host to ssh remote server ([email protected]) without a password.

    1. Create Authentication SSH-Keygen Keys on client.
    2. $ ssh-keygen -t rsa
      
    3. Create .ssh Directory on the remote server.
    4. $ ssh [email protected] mkdir -p .ssh
      
    5. Upload Generated Public Keys to remote server.
    6. $ cat /u/ainet/.ssh/id_rsa.pub | ssh [email protected]  'cat >> .ssh/authorized_keys'
      
    7. Set Permissions on remote server.
    8. $ ssh [email protected]  "chmod 700 .ssh; chmod 640 .ssh/authorized_keys"
      
    9. Test passwordless ssh connection.
    10. $ ssh [email protected]
      
    Reply
  2. Hi Ravi,

    Wonderful post! Thank you! I have a question. I would like to be able to do this for multiple devices (say ssh from a Linux computer into multiple Raspberry Pi computers) When I try to do this for another Pi device, the previous one is forgotten. How can I use what you are showing here for multiple devices?

    Reply
    • @Vincent,

      Create one Authentication SSH-Keygen Keys on your Linux server, and upload the Generated Public Key to multiple remote machines under .ssh directory.

      Reply
  3. Will these authorized_keys files be not expired even after patch deployment server restarts? Can you please reply to this?

    Reply
    • @Revathi,

      No these SSH authorized_keys files never expire and remain the same even after update or upgrade of server to newer releases…

      Reply
    • Step 2 assumes there isn’t already an ssh directory on the server.

      ssh-copy-id‘ is a shell script that will perform steps 2 and 3, but it is not present on every Linux device.

      Following the instruction in step 2 will work in any case.

      Reply

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