Connecting to Arjuna

Arjuna is located at arjuna.psc.edu to connect, enter the following into a terminal:

ssh andrewID@arjuna.psc.edu

To connect to Arjuna, you must either be on the campus network, connect via the linux timeshare, or using CMU’s Full VPN.

When you first log in to Arjuna, you will be prompted for a password. Enter the password given to you by the Administrator who created your account. You will be immediately required to change it.

Arjuna’s SSH key fingerprints

Public Key fingerprints are used to validate the connection to a remote server. When connecting to a server for the first time you will be prompted to verify the authenticity of the server, by comparing the server’s reported fingerprint to the expected fingerprint.

Arjuna’s public key fingerprints are:

You should not connect to Arjuna if the fingerprints do not match. Please open an issue

Accessing Arjuna via CMU’s Full VPN

If you are not on campus, you must first connect to CMU’s Full VPN. Once connected you can then ssh into Arjuna.

Configuring SSH

The following steps are quality-of-life improvements to default ssh configuration. They are not required to use Arjuna.

Private Key Authentication

Instead of authenticating using a password, you can authenticate using Private Key Authentication and skip typing in a password every time.

First, generate a set of keys to use in authentication. Skip this step if you already have a public/private key pair (Look for ~/.ssh/id_rsa);

ssh-keygen -t rsa

You will be prompted for a location to save your keys (The default is fine) and a passpharse to unlock your keys. Follow the prompts as directed.

Your private key ~/.ssh/id_rsa is your password. Treat it as such and do not copy it to insecure systems, display it in public space, etc.

Now that you have a key pair, we need to transfer the public key to Arjuna. To do so, run the following command:

ssh-copy-id andrewID@arjuna.psc.edu

You will be prompted for your key’s passphrase (if set) and your password for Arjuna. You can now log in without entering your password!

Using a SSH Config File

You can simplify logging in to Arjuna by creating an ~/.ssh/config file to specify common option (i.e. your username) or create an alias for Arjuna.

For example, the following config will let you connect with ssh arjuna instead of having to type out the full ssh andrewID@arjuna.psc.edu each time.

Host arjuna
    User andrewID
    HostName arjuna.psc.edu

Sample SSH Configuration File

The following is a sample ~/.ssh/config that enables some helpful features.

# The * wild card means these options apply everywhere
Host *
    # The next three options configure ssh to reuse sockets to the same host.
    # This speeds up your connection time when ssh in from multiple terminals
    # to the same host
    ControlMaster auto
    ControlPath ~/.ssh/sockets/%h-%p    # This is where ssh will save the sockets too
    ControlPersist 600                  # Key connection open for 600 seconds
    AddKeysToAgent yes              # Automatically adds keys to your ssh-agent
    IdentityFile ~/.ssh/id_rsa      # This set your default key for authentication

Host arjuna
    User andrewID
    ForwardAgent yes
    # Forward your SSH agent, so you use your machine's ssh-agent to authenticate
    # to other machines from Arjuna. This way you don't need to manage multiple
    # ssh keypairs to connect to a common service (i.e. GitHub)
    HostName arjuna.psc.edu

# Skip CMU's VPN and connect to Arjuna via unix.andrew.cmu.edu
# You will be prompted for your CMU password to login to unix.andrew.cmu.edu
# before being forwarded to Arjuna
Host arjuna-jump
    User andrewID
    ForwardAgent yes
    ProxyJump andrewID@unix.andrew.cmu.edu

For more configuration options see man ssh_config or ssh_config’s documentation.