How to permanently add a private key with ssh-add on Ubuntu?

1. Generate an SSH Key Pair (if you don't have one yet):
   If you don't have an SSH key pair, you can create a new one by running the following command:

   bash
   ssh-keygen -t rsa -b 4096  

   Follow the prompts to complete the key generation process. You can set a passphrase or leave it empty.

2. Add the Private Key to the SSH Agent:
   To have the SSH key automatically loaded at system startup, add it to the ssh-agent. First, ensure that ssh-agent is running:

   bash
   eval "$(ssh-agent -s)"  

   Then, use the ssh-add command to add the private key:

   bash
   ssh-add ~/.ssh/id_rsa  

   This assumes your private key file is ~/.ssh/id_rsa. If your key file name or path differs, modify the command accordingly.

3. Configure the ~/.ssh/config File:
   You can create or edit the ~/.ssh/config file to help manage and automate SSH connection settings. For example, you can specify which private key to use for a specific host:

   bash
   Host example.com  
     IdentityFile ~/.ssh/id_rsa  

   This ensures that the specified private key is used every time you connect to example.com.

4. Make the Key Automatically Load at System Startup:
   To have the private key automatically loaded at each system startup, add the ssh-add command to your .bashrc or .profile file:

   bash
   if [ -z "$(pgrep ssh-agent)" ]; then  
     eval $(ssh-agent -s)  
     ssh-add ~/.ssh/id_rsa  
   fi  

   This script checks if ssh-agent is running; if not, it starts ssh-agent and adds your private key.

By following these steps, your SSH private key will be automatically loaded at each login or system startup on Ubuntu, simplifying the SSH connection process. This is particularly useful when managing multiple servers or performing automated deployments.