Git is an open source, distributed version control system that is commonly used for collaboration on code or documents. While it is often used with a hosting service like GitHub, Git can be used locally to track changes within a single repository stored on disk.
Making Git Available
Git is available as part of the operating system, but that version of Git is old. It is strongly recommended that you load a newer version of Git with the git module before using Git:
module load git
Setting up Git
Before you use Git for the first time on Quest, you need to set the user name and email address it will use when it records your commits. Use the following commands to set this information:
git config --global user.name "John Doe"
git config --global user.email johndoe@northwestern.edu
You only need to do this one time. Git will remember your name and email.
To view your Git settings, at any time you can run this command:
git config --list
Repositories
You can create repositories at any time in any directory on Quest you have write access to with the git init command. However, if you wish to clone a repository from a remote server such as GitHub or Bitbucket, you have a choice of using either HTTPS or SSH to clone.
Cloning from GitHub with HTTPS
To clone a repository from GitHub on Quest using the HTTPS protocol, click the "Clone or download" button:
Then copy the URL that appears below it:
Finally, in your Quest terminal, run this command (pasting in the URL you copied):
git clone https://github.com/<organization>/<repository>.git
That will download the repository from GitHub into a directory with the same name as the repository.
If the repository is private (and you have access to it), you will be asked to provide your GitHub username and password. Similarly, if you push to a repository you have cloned from GitHub using the HTTPS protocol, you will have to provide your username and password. Because it is annoying to have to type your username and password over and over again, Git provides a way to cache your credentials.
Type the following command to enable username and password caching:
git config --global credential.helper cache
By default Git will remember your credentials for 15 minutes. To set a different timeout (in seconds), use a command like this one:
git config --global credential.helper 'cache --timeout=3600'
This will allow Git to remember your credentials for one hour.
Cloning from GitHub with SSH
To clone a repository from GitHub on Quest using the SSH protocol, you must first load your SSH key from Quest into GitHub.
First, in your Quest terminal, print out the contents of your SSH public key:
cat ~/.ssh/id_rsa.pub
This will display several lines of text. Copy it to your computer's clipboard, then go to GitHub and click your profile in the upper right corner, then click "Settings":
In the left sidebar, click "SSH and GPG Keys"
Click "New SSH Key"
In the "Title" field, enter a descriptive name for the key, such as "Quest". Paste the public key you copied earlier into the "Key" field, then click the "Add SSH Key" button. If prompted, confirm your GitHub password.
Now you are able to clone using the SSH protocol.
On the page of a repository you want to clone on GitHub, click "Clone or Download".
Then click the "Use SSH" link.
Next, copy the repository URL.
Finally, in your Quest terminal, run this command (pasting in the URL you copied):
git clone git@github.com/<organization>/<repository>.git
That will download the repository from GitHub into a directory with the same name as the repository. You will now be able to push and pull from this remote repository without having to enter a username and password.
Git Resources
There are many resources for learning Git on the web. See the Research Computing Git Workshop page for a list of resources.