Access to Server via SSH

On client, generate rsa key and add to ssh-agent

There are several ways to generate an rsa key pair, or you can use an existing one.

1. The GitHub way:

• Create a new ssh key, using your email as a label

  ssh-keygen -t rsa -b 4096 -C "[email protected]"
  # generating public/private rsa key pair.
  

• When you're prompted to Enter a file in which to save the key, press Enter. This accepts the default file location.

• At the Enter passphrase (empty for no passphrase) prompt, type a secure passphrase. A passphrase is a long word to identify your rsa key. It is okay to leave it blank and hit Enter.

• Before adding a new SSH key to the ssh-agent, you should have checked for existing SSH keys and generated a new SSH key.

  eval "$(ssh-agent -s)"
  # start the ssh-agent in the background
  

• Add your SSH key to the ssh-agent.

  ssh-add ~/.ssh/id_rsa
  

2. Use an Existing Key Pair

• Go to Terminal, type cd ~/.ssh and look for the pair of files that have the same name name but different extensions, eg. id_rsa and id_rsa.pub. They are your private key and public key.

• Keep the private key untouched, and copy the public key as a file to your Server.

• NOTE: Be sure to use the original .pub file instead of doing copy-paste keys!!

On Server, save public key and change user authorization

1. Copy your public key and rename it to authorized_keys under hidden folder .ssh.

   mkdir .ssh
   # skip this step if you already have it in your home directory
   
   chmod 700 .ssh
   # change the permission of folder .ssh
   
   cd .ssh
   touch authorized_keys
   chmod 600 authorized_keys
   # change the permission of file
   
   cat id_rsa.pub >> authorized_keys
   # concatenate id_rsa.pub to authorized_keys
   
   

2. Change user authorization

• Go to Terminal:

  cd /etc/ssh/
  sudo vim sshd_config
  

• On Line 90, add user to Allowusers

• Restart ssh to make changes valid

  sudo service sshd restart
  

Now connect your client machine to the server via SSH!

1. On Client, go to Terminal:

   ssh -1 -v username@hostIP
   

Or ssh -v -i ~/.ssh/id_rsa username@hostIP to indicate the location of key.

2. The next screen you will be on the Server!

Useful links

• GitHub: Generate a New SSH Key:

  [https://help.github.com/articles/generating-a-new-ssh-key-and-adding-it-to-the-ssh-agent/])

• Ubuntu help: SSH/OpenSSH/Keys:

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