How do I remove the passphrase for the SSH key without having to create a new key?

Short answer:

$ ssh-keygen -p

This will then prompt you to enter the keyfile location, the old passphrase, and the new passphrase (which can be left blank to have no passphrase).

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If you would like to do it all on one line without prompts do:

$ ssh-keygen -p [-P old_passphrase] [-N new_passphrase] [-f keyfile]

Important: Beware that when executing commands they will typically be logged in your ~/.bash_history file (or similar) in plain text including all arguments provided (i.e. the passphrases in this case). It is, therefore, is recommended that you use the first option unless you have a specific reason to do otherwise.

Notice though that you can still use -f keyfile without having to specify -P nor -N, and that the keyfile defaults to ~/.ssh/id_rsa, so in many cases, it's not even needed.

You might want to consider using ssh-agent, which can cache the passphrase for a time. The latest versions of gpg-agent also support the protocol that is used by ssh-agent.

$ ssh-keygen -p worked for me

Opened git bash. Pasted : $ ssh-keygen -p

Hit enter for default location.

Enter old passphrase

Enter new passphrase - BLANK

Confirm new passphrase - BLANK

BOOM the pain of entering passphrase for git push was gone.

Thanks!

You might want to add the following to your .bash_profile (or equivalent), which starts ssh-agent on login.

if [ -f ~/.agent.env ] ; then
    . ~/.agent.env > /dev/null
    if ! kill -0 $SSH_AGENT_PID > /dev/null 2>&1; then
        echo "Stale agent file found. Spawning new agent… "
        eval `ssh-agent | tee ~/.agent.env`
        ssh-add
    fi 
else
    echo "Starting ssh-agent"
    eval `ssh-agent | tee ~/.agent.env`
    ssh-add
fi

On some Linux distros (Ubuntu, Debian) you can use:

ssh-copy-id -i ~/.ssh/id_dsa.pub username@host

This will copy the generated id to a remote machine and add it to the remote keychain.

You can read more here and here.