The ssh-agent is caching your keys’ in memory once these are unlocked and you will not be asked to provide the passphrase to unlock these keys every time they are used.

Starting the agent

Depending on your operating system, there are multiple ways to start the agent, e.g. to start it manually in a bash-like shell, simply run

eval $(ssh-agent)

This command will start the agent and set-up the necessary environment variables. Please note that starting a new agent will make an already existing agent not directly accessibly anymore while NOT terminating it. Thus, please test via ssh-add -l if an agent is currently running (see below).

If you want your agent to be started automatically when logging in, please refer to the web, e.g. this question on stackoverflow.com for more information.

Typically, what you need to do is to ensure the agent is started and “primed” with your keys whenever you start a terminal ssh session. Putting a snippet like this into your ~/.bashrc ought to work for most people, but if you used a different shell or some other special tools, your solution may need to look different than this one:

# ensure the ssh agent is running
if [[ -z "$SSH_AUTH_SOCK" ]]
then
    eval $(ssh-agent)
fi

# list all keys here which should be loaded into the agent
for k in ~/.ssh/id_ed25519-atlas ~/.ssh/id_rsa
do
    if ! ssh-add -l | grep -q "$(ssh-keygen -lf "$k" | cut -d' ' -f 2)"
    then
        ssh-add "$k"
    fi
done

Which keys are currently handled by my agent?

Running ssh-add -l will display all keys currently known to your agent. If the list is empty, you have an ssh-agent running, but no keys currently unlocked. If you receive an error message like Could not open a connection to your authentication agent. you need to start the agent first (see above).

If you key is missing, simple add it via

ssh-add ~/.ssh/id_ed25519-atlas

and it will prompt you for the passphrase. Afterwards, the newly added key should be displayed by ssh-agent -l,

As always, reading the man pages for ssh-agent and ssh-add is recommended!