SSH Key-Pairs.

Remotely Connect to Linux Servers with SSH key-pairs

SSH: Authentication with Key-pairs

On your client machine:

  • Create ssh key pair by using the command ssh-keygen
    • It will create 2 files (Private key and Public key) in the .ssh folder.
[menit@fedora .ssh]$ ls 
id_rsa id_rsa.pub
  • It is recommended that you will use a passphrase to encrypt your private key
[menit@fedora .ssh]$ ssh-keygen 
Generating public/private rsa key pair.
Enter file in which to save the key (/home/menit/.ssh/id_rsa): 
Enter passphrase (empty for no passphrase): 
Enter same passphrase again: 
Your identification has been saved in /home/menit/.ssh/id_rsa
Your public key has been saved in /home/menit/.ssh/id_rsa.pub
The key fingerprint is:
SHA256:E+n8J9Sjbdbi5A7uyu7LVAm2Y8fNBtSawvCyoR7l3Y4 menit@fedora
The key's randomart image is:
+---[RSA 3072]----+
|          ..     |
|      .  o  .    |
|       += .o     |
|      +++=o*     |
|     + =So* *    |
|    o o..B.+ o   |
|   . .  .o= B .  |
|    .  +E..X .   |
|       oB+o.+    |
+----[SHA256]-----+
```

How to Deploy your public key to your manage servers.

  • To connect to your Linux servers using ssh keys you will need to transfer the public key to your remote servers

There are 2 methods to transfer the public key to your server

The first method is to install the public key from your own host to your remote server using this command:

  • This command will create on the remote host .ssh folder and a file named authorized_keys and he will copy-paste the public key to this file.
ssh-copy-id -i /home/menit/.ssh/id_rsa.pub username@192.168.122.235

  • The second method is to copy your public key and paste it to your remote server under the .ssh folder to file named authorized_keys (if you can’t find such file you just need to create it.

Now you can connect to your machine using this command

[menit@fedora .ssh]$ ssh swarm@192.168.122.235

Connect to your remote server without the passphrase

To avoid the need to enter a passphrase every time you ssh to a remote host you can use sshagent to Cache your Authentication Credentials into the host memory.

[menit@fedora .ssh]$ ssh-agent bash
[menit@fedora .ssh]$ ssh-add id_rsa
Enter passphrase for id_rsa: ***********
Identity added: id_rsa (menit@fedora)

How to ssh to a remote host using the Root User account.

  1. On the remote host, you will need first to enable the login as root option: To enable it to remove # from the line “PermitRootLogin prohibit-password”
swarm@swarm3:/etc/ssh$ vim /etc/ssh/sshd_config

#LoginGraceTime 2m
PermitRootLogin prohibit-password
#StrictModes yes
#MaxAuthTries 6
#MaxSessions 10

Exit and Save the file by pressing :wq

  1. Switch to you root account in the remote server and pass the Public ssh key to the authorized_keys file under the .ssh folder.
root@swarm3:~/.ssh# ls
authorized_keys

How to type sudo command with a password

To grant you user sudo permissions you will need to edit this config file:

[menit@fedora .ssh]$ sudo visudo

Under Allow people in group wheel paste this command

#Allow users to run all commands
menit ALL=(ALL) NOPASSWD: ALL

This is how it’s should be looked like in the config file:

## Allows people in group wheel to run all commands
%wheel  ALL=(ALL)       ALL

#Allow users to run all commands
menit ALL=(ALL) NOPASSWD: ALL

It’s important you enter your new line entry at the bottom of the config file because the visudo file is processed from the top to bottom.

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