Design and Analysis of Algorithms

Setting up/Using Git for Handing in Assignments

Goals for this week:

  1. Set up our Swarthmore GitHub accounts.
  2. Fill out a short informational questionnaire.
  3. Make sure you can grab, edit, submit assignments using git.

One-time git / GitHub configuration

Before using Swarthmore's GitHub Enterprise, you'll need to complete the following configuration steps once:

1. Create an ssh key

SSH (Secure SHell) is a mechanism that allows you to interact with remote machines and issue commands to them. It typically uses a username and password, but in some cases (and this is one of them), you need something else: a cryptographic key.

If you already have an ssh key, you can skip this step. If you're not sure, you probably do not already have a key. You can check by issuing the command:

ls -l -a ~/.ssh

If you see files named id_rsa and, you already have a key. If those files aren't there, or you're told that you have no such directory named .ssh, you'll need to generate a key.

GitHub has a good comprehensive guide on the subject, but I'll give you the executive summary below:

Run the command ssh-keygen. This will give you the output:

 $ ssh-keygen
 Generating public/private rsa key pair.
 Enter file in which to save the key (/home/[username]/.ssh/id_rsa):

Press enter to confirm the default location of /home/[username]/.ssh/id_rsa. Next, it'll ask you for a passphrase:

 Enter passphrase (empty for no passphrase):
 Enter same passphrase again:

Set a passphrase that you'll remember and then confirm it a second time. After confirming your passphrase, it'll print a key fingerprint and some strange abstract ASCII artwork that you can safely ignore.

2. Log in to Swarthmore's GitHub Enterprise and add your key.

Next, we need to let GitHub know about this key we just created. Head over to and log in using your typical Swarthmore account credentials (same account you use for email). It may ask for your name, email address, or other information. Fill that in.

When you're properly logged in, click the small gear icon at the top right of the page to get to your account settings. Choose SSH Keys from the menu on the left. Click the Add SSH key button, and two boxes will appear. Fill in the name with anything you like, this is just to help you remember where you generated the key. I would suggest a name like CS account.

After you've named your account, you need to copy in the entire contents of the file that you generated earlier. Make sure you use the file ending in .pub. You can dump the contents of the file by executing:

 more ~/.ssh/

Copy the entire output of that file, paste it into the Key box on GitHub, and click Add Key.

3. Git client user configuration settings

Before you starting using the git command on the command line, you need to give it a basic configuration. This will tell git who you are, making it easy for you and your partner to identify who committed code to your shared repository.

Replace the email and name strings with your email address and name. If you have not run these commands, then the very first git commit will fail and tell you to run them.

git config --global ""
git config --global  "Your Name"
git config --global push.default simple

That's it for now. We'll come back to git again after we go over a few examples.

4. Example Workflow

mkdir cs41
cd cs41
git clone hw00
cd hw00
emacs hw00.txt  #fill out questionnaire
git add hw00.txt
git commit -m "submitting hw 00"
git push