# Remotes in Github Version control really comes into its own when we begin to collaborate with other people. We already have most of the machinery we need to do this; the only thing missing is to copy changes from one repository to another. Systems like Git allow us to move work between any two repositories. In practice, though, it’s easiest to use one copy as a central hub, and to keep it on the web rather than on someone’s laptop. Most programmers use hosting services like [GitHub](https://github.com/), [Bitbucket](https://bitbucket.org/) or [GitLab](https://about.gitlab.com/) to hold those main copies; we’ll explore the pros and cons of this in a later episode. Let’s start by sharing the changes we’ve made to our current project with the world. To this end we are going to create a remote repository that will be linked to our local repository. ### Create a remote repository Log in to [GitHub](https://github.com/), then click on the icon in the top right corner to create a new repository called practiceGitHub:
Name your repository “practiceGitHub” and then click “Create Repository”. Note: Since this repository will be connected to a local repository, it needs to be empty. Leave “Initialize this repository with a README” unchecked, and keep “None” as options for both “Add .gitignore” and “Add a license.” See the “GitHub License and README files” exercise for a full explanation of why the repository needs to be empty.
As soon as the repository is created, GitHub displays a page with a URL and some information on how to configure your local repository:
This effectively does the following on GitHub’s servers: ``` mkdir practiceGitHub cd practiceGitHub git init ``` Now that we have two repositories, we need a diagram like this:
Note that our local repository still contains our earlier work on practicegit, but the remote repository on GitHub appears empty as it doesn’t contain any files yet. ### Connect local to remote repository Now we connect the two repositories. We do this by making the GitHub repository a remote for the local repository. The home page of the repository on GitHub includes the URL string we need to identify it:
Click on the ‘SSH’ link to change the [protocol](https://swcarpentry.github.io/git-novice/reference.html#protocol) from HTTPS to SSH. * HTTPS vs. SSH ``` We use SSH here because, while it requires some additional configuration, it is a security protocol widely used by many applications. The steps below describe SSH at a minimum level for GitHub. ```
Copy that URL from the browser, go into the local practicegit repository, and run this command: ``` git remote add origin git@github.com:BMCBCC/practiceGitHub.git ``` Make sure to use the URL for your repository rather than ours: the only difference should be your username instead of BMCBCC. origin is a local name used to refer to the remote repository. It could be called anything, but origin is a convention that is often used by default in git and GitHub, so it’s helpful to stick with this unless there’s a reason not to. We can check that the command has worked by running git remote -v: ``` git remote -v ``` Output ``` origin git@github.com:BMCBCC/practiceGitHub.git (fetch) origin git@github.com:BMCBCC/practiceGitHub.git (push) ``` We’ll discuss remotes in more detail in the next episode, while talking about how they might be used for collaboration. ### SSH background and setup Before we can connect to a remote repository, we need to set up a way for our computer to authenticate with GitHub so it knows it’s us trying to connect to our remote repository. We are going to set up the method that is commonly used by many different services to authenticate access on the command line. This method is called Secure Shell Protocol (SSH). SSH is a cryptographic network protocol that allows secure communication between computers using an otherwise insecure network. SSH uses what is called a key pair. This are two keys that work together to validate access. One key is publicly known and called the public key, and the other key called the private key is kept private. Very descriptive names. You can think of the public key as a padlock, and only you have the key (the private key) to open it. You use the public key where you want a secure method of communication, such as your GitHub account. You give this padlock, or public key, to GitHub and say “lock the communications to my account with this so that only computers that have my private key can unlock communications and send git commands as my GitHub account.” What we will do now is the minimum required to set up the SSH keys and add the public key to a GitHub account. The first thing we are going to do is check if this has already been done on the computer you’re on. Because generally speaking, this setup only needs to happen once and then you can forget about it. * Keeping your keys secure ``` You shouldn’t really forget about your SSH keys, since they keep your account secure. It’s good practice to audit your secure shell keys every so often. Especially if you are using multiple computers to access your account. ``` We will run the list command to check what key pairs already exist on your computer.
``` ls -al ~/.ssh ``` Your output is going to look a little different depending on whether or not SSH has ever been set up on the computer you are using. If you have not set up SSH on his computer, the output is ``` ls: cannot access '/c/Users/Username/.ssh': No such file or directory ``` If SSH has been set up on the computer you’re using, the public and private key pairs will be listed. The file names are either id\_ed25519/id\_ed25519.pub or id\_rsa/id\_rsa.pub depending on how the key pairs were set up. If they don’t exist, you need to create them. #### Create an SSH key pair ``` drwx------ 2 duan ki-bcc 136 Mar 2 20:24 . drwxr-xr-x 58 duan ki-bcc 4096 Mar 1 17:56 .. -rw------- 1 duan ki-bcc 444 Mar 2 20:24 id_ed25519 -rw-r--r-- 1 duan ki-bcc 94 Mar 2 20:24 id_ed25519.pub ``` Output ``` ls -al ~/.ssh ``` Now that we have generated the SSH keys, we will find the SSH files when we check. The “identification” is actually the private key. You should never share it. The public key is appropriately named. The “key fingerprint” is a shorter version of a public key. ``` Your identification has been saved in /home/duan/.ssh/id_ed25519. Your public key has been saved in /home/duan/.ssh/id_ed25519.pub. The key fingerprint is: ec:b1:d8:59:34:f1:2b:b2:63:2b:bf:0b:3d:92:06:b1 duan@mit.edu The key's randomart image is: +--[ED25519 256--+ | . | | o | | . o . | | o . . . . | | E S o . | | . * B . | | * @ | | ..+ + | | o=o | +-----------------+ ``` After entering the same passphrase a second time, we receive the confirmation ``` Enter same passphrase again: ``` Output Now, it is prompting us for a passphrase. To be safe, let's create a passphrase. Be sure to use something memorable or save your passphrase somewhere, as there is no “reset my password” option. ``` Created directory '/home/duan/.ssh'. Enter passphrase (empty for no passphrase): ``` Output We want to use the default file, so just press Enter. ``` Generating public/private ed25519 key pair. Enter file in which to save the key (/home/duan/.ssh/id_ed25519): ``` Output If you are using a legacy system that doesn’t support the Ed25519 algorithm, use: $ ssh-keygen -t rsa -b 4096 -C "" ``` ssh-keygen -t ed25519 -C "duan@mit.edu" ``` To create an SSH key pair we use this command, where the -t option specifies which type of algorithm to use and -C attaches a comment to the key (here, our email) #### Copy the public key to GitHub Now we have a SSH key pair and we can run this command to check if GitHub can read our authentication. ``` ssh -T git@github.com ``` Output ``` Permission denied (publickey). ``` Right, we forgot that we need to give GitHub our public key! First, we need to copy the public key. Be sure to include the .pub at the end, otherwise you’re looking at the private key. ``` cat ~/.ssh/id_ed25519.pub ``` Output ``` ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAIKRkTUE8ksBlseYf6YOsgnAD0geKZGuhiBapcY9VLAF6 duan@mit.edu ``` Now, going to GitHub.com, click on your profile icon in the top right corner to get the drop-down menu. Click “Settings,” then on the settings page, click “SSH and GPG keys,” on the left side “Account settings” menu. Click the “New SSH key” button on the right side. Now, you can add the title (We use the title “cluster home directory” so we can remember where the original key pair files are located), paste your SSH key into the field, and click the “Add SSH key” to complete the setup. Now that we’ve set that up, let’s check our authentication again from the command line. ``` eval `ssh-agent -s` ssh-add ~/.ssh/id_ed25519 ssh -T git@github.com ``` Output ``` Hi BMCBCC! You've successfully authenticated, but GitHub does not provide shell access. ``` Good! This output confirms that the SSH key works as intended. We are now ready to push our work to the remote repository. #### Push local changes to a remote Now that authentication is setup, we can return to the remote. This command will push the changes from our local repository to the repository on GitHub: ``` git push origin main ``` Output ``` Counting objects: 22, done. Delta compression using up to 32 threads. Compressing objects: 100% (18/18), done. Writing objects: 100% (22/22), 2.24 KiB | 0 bytes/s, done. Total 22 (delta 4), reused 0 (delta 0) remote: Resolving deltas: 100% (4/4), done. To git@github.com:BMCBCC/practiceGitHub.git * [new branch] main -> main ``` * Proxy If the network you are connected to uses a proxy, there is a chance that your last command failed with “Could not resolve hostname” as the error message. To solve this issue, you need to tell Git about the proxy: ``` git config --global http.proxy http://user:password@proxy.url git config --global https.proxy https://user:password@proxy.url ``` When you connect to another network that doesn’t use a proxy, you will need to tell Git to disable the proxy using: ``` git config --global --unset http.proxy git config --global --unset https.proxy ``` * Password Managers If your operating system has a password manager configured, git push will try to use it when it needs your username and password. For example, this is the default behavior for Git Bash on Windows. If you want to type your username and password at the terminal instead of using a password manager, type: ``` unset SSH_ASKPASS ``` in the terminal, before you run git push. Despite the name, [Git uses SSH\_ASKPASS for all credential entry](https://git-scm.com/docs/gitcredentials#_requesting_credentials), so you may want to unset SSH\_ASKPASS whether you are using Git via SSH or https. You may also want to add unset SSH\_ASKPASS at the end of your \~/.bashrc to make Git default to using the terminal for usernames and passwords.
* The '-u' Flag You may see a -u option used with git push in some documentation. This option is synonymous with the --set-upstream-to option for the git branch command, and is used to associate the current branch with a remote branch so that the git pull command can be used without any arguments. To do this, simply use git push -u origin main once the remote has been set up. We can pull changes from the remote repository to the local one as well: ``` git pull origin main ``` Output ``` From github.com:BMCBCC/practiceGitHub * branch main -> FETCH_HEAD Already up-to-date. ``` Pulling has no effect in this case because the two repositories are already synchronized. If someone else had pushed some changes to the repository on GitHub, though, this command would download them to our local repository. --- # Agent Instructions: Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question. Perform an HTTP GET request on the current page URL with the `ask` query parameter: ``` GET https://igb.mit.edu/mini-courses/version-control-with-git/remotes-in-github.md?ask= ``` The question should be specific, self-contained, and written in natural language. The response will contain a direct answer to the question and relevant excerpts and sources from the documentation. Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.