Setup Passwordless SSH in Linux
Simplify remote logins by setting up passwordless SSH.
Every time you ssh from one Linux server to another, you need to enter target server user's password. We can also setup passwordless ssh in Linux between two Linux servers so that you don't have to enter password for the target server user.
Overview
We have two Linux servers (192.168.1.181 and 192.168.1.182) and we will be setting ssh without password between the two Linux servers for root user.
Note: the process remains exactly same for setting up passwordless ssh for any other user in Linux.
Verify Existing SSH-Keys
It is a good idea to first check if ssh-keys are already generated on Linux server. You can always re-use the existing ssh keys and regenerating ssh keys will not be a good idea.
Let us check ssh-key on our servers (192.168.1.181 and 192.168.1.182)
On 191.168.1.181
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ls -al ~/.ssh/id_*.pub
On 192.168.1.182
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ls -al ~/.ssh/id_*.pub
If you see existing ssh keys then, skip the next step and move to Add SSH-Keys
Else, proceed below!
Generate SSH-Keys
In each server, generate the ssh keys using ssh-keygen utility in linux
On 192.168.1.181
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ssh-keygen
Enter file in which to save the key (/root/ .ssh/id_rsa): [Press enter key]
Enter passphrase (empty for no passphrase): [Press enter key]
Enter same passphrase again: [Press enter key]
Your identification has been saved in /root/ .ssh/id_rsa.
Your public key has been saved in /root/ .ssh/id_rsa.pub.
On 192.168.1.182
================
ssh-keygen
Enter file in which to save the key (/root/ .ssh/id_rsa): [Press enter key]
Enter passphrase (empty for no passphrase): [Press enter key]
Enter same passphrase again: [Press enter key]
Your identification has been saved in /root/ .ssh/id_rsa.
Your public key has been saved in /root/ .ssh/id_rsa.pub.
Add SSH-Keys
View the ssh keys on 192.168.1.181 server and copy them to notepad
On 192.168.1.181
================
cat ~/.ssh/id_rsa.pub
View the ssh keys on 192.168.1.182 server and copy them to notepad
On 192.168.1.182
================
cat ~/.ssh/id_rsa.pub
Your keys must look like below on notepad
Copy the above keys from notepad and put it under .ssh/authorized_keys file on both server
On 192.168.1.181
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vi ~/.ssh/authorized_keys --> paste keys from notepad
On 192.168.1.182
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vi ~/.ssh/authorized_keys --> paste keys from notepad
Set Permissions
Give permissions to .ssh and authorized_keys file on both servers
On 192.168.1.181
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chmod 700 ~/.ssh
chmod 600 ~/.ssh/authorized_keys
On 192.168.1.182
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chmod 700 ~/.ssh
chmod 600 ~/.ssh/authorized_keys
Test Passwordless SSH
Let's connect from 192.168.1.181 to 192.168.1.182 to check if ssh without password is working
On 192.168.1.181
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ssh root@192.168.1.182
The authenticity of host '192.168.1.182 (192.168.1.182)' can't be established. ECDSA key fingerprint is SHA256:6yPNygL8ho6JKSlz54LFRzDSNf6UdBUQZcsWaqig738. ECDSA key fingerprint is MD5:c0:28:a8:2e:77:86:bb:cd:07:e4:c9:8e:3b:8f:de:43. [Enter yes Here] yes
Let's connect from 192.168.1.182 to 192.168.1.181 server
On 192.168.1.182
================
ssh root@192.168.1.181
The authenticity of host '192.168.1.181 (192.168.1.181)' can't be established. ECDSA key fingerprint is SHA256:6yPNygL8ho6JKSlz54LFRzDSNf6UdBUQZcsWaqig738. ECDSA key fingerprint is MD5:c0:28:a8:2e:77:86:bb:cd:07:e4:c9:8e:3b:8f:de:43. [Enter yes Here] yes
Done! we have a passwordless ssh login setup done for the root user.
Further read