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Generate SSH Key pair & Add to Agent

SSH from one ec2 to another ec2. Generate key and SSH from one VM to another VM.

Step 1

Generate key in your client machine/laptop

ssh-keygen -t ed25519 -a 100 -C [add a comment or username]
or non-interactively
ssh-keygen -t ed25519 -a 100 -C $FILENAME -f ~/.ssh/$FILENAME -N ''

Step 2: Linux & Mac

Add the key to your ssh-agent. Doing this will make life easier. You will not have to provide a private key during ssh in the terminal

eval $(ssh-agent -s)

ssh-add ~/.ssh/id_rsa
Step 2: Windows
# By default the ssh-agent service is disabled. Allow it to be manually started for the next step to work.
# Make sure you're running as an Administrator.
Get-Service ssh-agent | Set-Service -StartupType Manual

# Start the service
Start-Service ssh-agent

# This should return a status of Running
Get-Service ssh-agent

# Now load your key files into ssh-agent
ssh-add ~\.ssh\id_rsa
Step 3

Now copy the contents of the file to the clipboard.

cat ~/.ssh/

Step 4

In the remote server in which you want to SSH/setup SSH. It might sound funny/confusing, but yes you need to access this system (i.e. login with SSH or user-password) and modify some files. Without this, you cannot proceed further.

echo "PASTE CONTENTS OF FILE HERE" >> ~/.ssh/authorized_keys
Step 5

Now everything is ready You can now ssh from your client to a remote machine with just one command. Replace username with your remote machine username and replace your IP address.