SSH Access and Key Pairs

When working with our Unix servers from a Mac, the first step is to establish an SSH connection from the command line in the Terminal application to one of our login servers. To find the Terminal app, either open your Finder and navigate to Applications or do a spotlight search (⌘ + spacebar) and type "terminal" to find the application.

If you are just starting at DS, you should have already done this process to set your Unix password, as part of your onboarding setup steps.

With Terminal open, you are now at the command line of your Mac! The next step is to type the following command, adapted to your username and the desired login server. The underlined text will need to be edited when running the command.

ssh username@servername.dfci.harvard.edu

When prompted, enter your Unix password. If you are returning to Unix after some time off and forget the password, contact our team.

In practice, with the username john and target server ada, we run the command as:

ssh john@ada.dfci.harvard.edu

Depending on if we already configured our SSH keys, we should be all set.

List of login servers

• ada.dfci.harvard.edu - no large jobs here please!

• noah.dfci.harvard.edu 

• leo.dfci.harvard.edu

• lynx.dfci.harvard.edu

• lyra.dfci.harvard.edu - use this system for file transfers!

• libra.dfci.harvard.edu

• orion.dfci.harvard.edu

• ara.dfci.harvard.edu

• lepus.dfci.harvard.edu

NOTE: Steps 1 - 3 are for users who do not already have PuTTY installed.

1. On your Windows device, download PuTTY from the official website.

2. As you should be on Windows 10 or 11, download the first file in the Packages section (64-bit x86) by clicking on the blue link that reads:
   putty-64bit-0.XX-installer.msi (where XX = version). Accept all warnings and do a default installation.

   • This will be the most current version on their site.

3. Once downloaded, run the .msi file to install PuTTY and related utilities, including puttygen for SSH key pair generation if RSA key authentication is desired or required.

4. With PuTTY now installed, you can open it by pressing the Windows key and searching "putty". It's advised to pin it to your taskbar or start menu. Launch the application when you're ready to proceed.

NOTE: These steps require PuTTY and PuTTYGen be installed on your Windows machine.

1. Navigate to the Start Menu or press your Windows key and begin typing putty to find PuTTYGen.exe in the results. Once located, start the program.

   • If PuTTYGen.exe is not already installed on your Windows device, you can click here to download it individually.

2. With it now installed, you can open it by pressing the Windows key and searching "putty" and clicking the program named "PuTTYGen". Launch the application when you're ready to proceed.

3. You will be prompted with a PuTTYGen window and should see the option to generate a new key. We want to generate a new key of type RSA with 4096 as the number of bits (this will default to 2048, overwrite it with 4096 which is 2048 x 2!). Set the bits to 4096 before clicking "Generate" and then have some fun moving your mouse around as instructed.

4. Once generated, you may opt to include a passphrase that you will then have to enter every time you connect using the key.

5. Press the Save private key button. PuTTYgen will put up a dialog box asking you where to save the file. Select a folder such as My Documents or your local home directory, and press Save. This file is in PuTTY’s native format (*.PPK); it is the one you will need to configure in PuTTY.exe.

6. Next, highlight and copy the Public key for pasting into OpenSSH authorized_keys file" - see screenshot below. Please email systems@ds.dfci.harvard.edu with the text enclosed there. Click Save public key to save your public key file to a memorable location. 

1. Open a new Terminal window, if one is not open already. You should not be logged into any servers when following step 2.

   • Click the magnifying glass in the upper right corner of your Mac's screen, on the top bar by the clock/Wifi/battery icons. This will open the Spotlight search on your Mac, which helps locate applications and files all across your machine.

   • Type "Terminal" to find the Terminal app.

2. Welcome to the command line! Next, we will generate the SSH key pair:
   ssh-keygen -t rsa -b 4096

3. Press Enter one more time to save your SSH key pair in the default location (your MacOS directory) with 3 important pieces:
   ~/.ssh/ 📁 This hidden directory contains files enabling you to go from ada/noah to other servers that require key pair authentication.
   ~/.ssh/id_rsa.pub ✅ This is your PUBLIC key. You may share this with the Systems team in step  
   ~/.ssh/id_rsa 🛑 This is your PRIVATE key. Don't share this with anyone.

4. You will be prompted to enter a secure passphrase, which is optional. If you go with a passphrase, make sure to remember it, as it will need to be entered every time you remotely log into a system via SSH using this key pair.

5. Now that we've completed the keygen steps, you now have two new files in your ~/.ssh/ directory: id_rsa and id_rsa.pub.

6. We will only share the .pub (pubkey) file, so please copy and paste the file into a new email to systems@ds.dfci.harvard.edu (step 8).

7. To get to the id_rsa.pub file and add it as an email attachment or view it, run the following command in Terminal:
   open ~/.ssh

   • The command above will open a Finder window where you can see both files. Only ever share the .pub file, not the other one called 'id_rsa' as that is your private key!

   • Alternatively, you can send the full output of the following command and share it via email if you want us to help configure it:
     cat ~/.ssh/id_rsa.pub

   • Make sure the beginning of the output says ssh-rsa. Copy and paste the entire thing when sending it to us, from ssh-rsa to the end.

8. The Systems team can help configure your Unix account to use this key for logging into Unix servers once we receive your email and notify you when done.

9. If you are feeling adventurous and want to do it yourself -- and you know your Unix password currently -- log into any server such as ada or noah and run the following commands:

   • mkdir ~/.ssh

   • If the command above says the directory already exists, that's fine too. Continue running the commands as listed:

   • chmod 700 ~/.ssh

   • cd ~/.ssh

   • pwd

   • The command above, pwd, will print working directory and confirm you are in fact inside your .ssh folder.

   • touch authorized_keys

   • chmod 600 authorized_keys

   • vim authorized keys

   • Now in Finder we right click the id_rsa.pub file and select Open with... then select the built-in TextEdit program or other text editor software of your choice such as SublimeText, etc.

   • Press command+a to select all text in the file, and with it highlighted press command+c to copy. 

   • Return to your vim tab in Terminal and press i to insert (be able to type), then command+V to paste the string of text inside. Press the following sequence of keys to save and exit vim (if you get tripped up here, start over and make a new authorized_keys file!):

   • esc

   •   : [AKA colon, requires holding shift key. This will appear in the bottom left corner of the window.]

   • wq [this should appear in the bottom left corner beside the colon character.]

   • return (enter)

   • And you've just used vim to paste in your public key, then successfully told it to write and quit the file editor interface! Way to go. Test with a new ssh connection and contact Systems if you encounter any issues.