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SSH - Secure Shell

  • What is SSH?
    • Full form → secure shell
    • Its works as a communication protocol & helps to connect with a remote computer
    • We can do anything on remote computer
      • File changes
      • Data changes
      • Setting up web servers
    • Main feature → Traffic is encrypted (thats why called secure shell)
    • Used mostly in the terminal/command line
  • Client/Server Communication
    • SSH → client
    • SSHD → server (OpenSSH Daemon)
      • listens for SSH connections
      • servers have SSHD config files
    • Servers have SSHD installed & running → required to make a connection using SSH
  • Authentication Methods
    • Authenticating servers using ssh
    • Ways:

      1. Password

        • default method

        • creating a user on a remote server & logging in using ssh & the password for that use

        • Example:

          ssh kunal@192.168.1.29

      2. Public/Private Key Pair

        • recommended way to logging in to the remote server
        • we can generate public & private keys
        • this is a safer approach as compared to having passwords

      3. Host Based

        • Pre-defining the hosts that are allowed to connect to a machine
        • Defined in a file called as known_hosts
          • client file containing all remotely connected known hosts , and the ssh client uses this file. This file authenticates for the client to the server they are connecting to. The known_hosts file contains the host public key for all known hosts.
  • Generating SSH keys

    • Command used:

      ssh-keygen
      • ~/.ssh/id_rsa (Private Key)
      • ~/.ssh/id_rsa.pub (Public Key)

    • Public key goes into the server → in authorized_keys file

  • For Windows users
    • Windows 10 supports native SSH
    • Git Bash & other terminal programs include ssh command & other UNIX tools

Hands-On & Cheat Sheet

Login via SSH with password (LOCAL SERVER)

  • Logging in to the local server
    • ssh kunal@192.168.1.29
      • kunal → name of the user that we wanna login as (already created in the local server)
      • 192.168.1.29 → IP address of the local server
  • Generating SSH Keys
    • ssh-keygen
  • Copying the public key to the server

    • Using the command:

      ssh-copy-id username@remote_host
      • The ssh-copy-id tool is included by default in many operating systems, so you may have it available on your local system.

    • Alternative method:

      cat ~/.ssh/id_rsa.pub | ssh username@remote_host "mkdir -p ~/.ssh && touch ~/.ssh/authorized_keys && chmod -R go= ~/.ssh && cat >> ~/.ssh/authorized_keys"

Using SSH to log in to a remote server (created using service providers)

  • Various cloud-service providers:

    • Digital Ocean
    • Linode
    • AWS
    • Hostwinds

  • Using Linode today!

    • Generating new keys:

      ssh-keygen -t rsa
      • You can give custom names to each pair of key files you generate
        • By default, the name would be id_rsa & id_rsa.pub
      • In our case, lets name them with id_rsa_lo

      • Therefore, the 2 keys generated:
        • id_rsa_lo
        • id_rsa_lo.pub

    • Adding the public SSH key to Linode:

    • Remote server is created successfully 🎉

    • Its time to log in to our server using ssh

      • Using the IP address
      ssh root@170.187.250.90

      • We are in our Ubuntu Remote Server

    Using Ubuntu in a remote server

    • Updating & Upgrading all the packages is a good practice once you create your server

      sudo apt update
      sudo apt upgrade

    • Creating a new user → again, always a good practice to not use the root user for working

      adduser <name>

    • To check the info of the new user → Example: kunal

      id kunal

# Ouput:
uid=1000(kunal) gid=1000(kunal) groups=1000(kunal)

    • Adding sudo priviledges to a new user

      usermod -aG sudo kunal

      • Checking the above:

        id kunal

# Output:
uid=1000(kunal) gid=1000(kunal) groups=1000(kunal),27(sudo)
        • 27(sudo) → sudo permissions have been added

    • Logging in to the server (again) as a new user (kunal)

      ssh kunal@170.187.250.90

    • Disabling the root user login now:

      1. Heading over the config file location
      sudo nano /etc/ssh/sshd_config

      1. Setting the value of PermitRootLogin as → no

      2. Reloading SSHD service

        sudo systemctl reload sshd

    Creating an Apache server on the remote server

    • Installing Apache

      apt install apache2 -y
      • -y → yes to everything (assumes the answers to all the prompts as YES)

    • We can now open up our IP address on the browser & will have Apache server running

Using Git & GitHub on the remote Ubuntu server

  • Setting up SSH keys for GitHub

    ssh-keygen -t rsa
    • We can name these as:
      • id_rsa_gh
      • id_rsa_gh.pub

  • Adding our public key to GitHub (in our host server)

  • Using ssh-add command to add SSH private keys into the SSH authentication agent

    • To add the ssh-agent, for using ssh-add

      eval `ssh-agent -s`

    • Using ssh-add:

      ssh-add /home/kunal/.ssh/id_rsa_gh

    • We now have our GitHub identity added

  • We can now clone the repository (on which we have added the ssh public key)

    • Example:

      git clone git@github.com:verma-kunal/PingIO

  • Installing Node Js on Ubuntu:
    • Used the documentation here