ARC Training

Remotes in GitHub

Overview

• Teaching: 30 min
• Exercises: 0 min

Questions

• How do I share my changes with others (on the web)?

Objectives

• Explain what remote repositories are and why they are useful.
• Push to or pull from a remote repository.

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, BitBucket or GitLab to hold those master copies; we’ll explore the pros and cons of this in the final section of this lesson.

Let’s start by sharing the changes we’ve made to our current project with the world. Log in to GitHub, then click on the icon in the top right corner to create a new repository called planets:

Name your repository planets, add an optional description and the click Create Repository.

As soon as the repository is created, GitHub displays a page with a URL and some information on how to configure your local repository:

which effectively does the following on GitHub’s servers:

% mkdir planets
% cd planets
% git init

Our local repository contains our earlier work on mars.txt, but the remote repository on GitHub doesn’t contain any files yet:

The next step is to 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 string we need to identify it:

Click on the HTTPS link to change the protocol from SSH to HTTPS if needed.

HTTPS vs. SSH

We use HTTPS here because it does not require additional configuration. After the workshop you may want to set up SSH access, which is a bit more secure, by following one of the great tutorials from GitHub, Atlassian/BitBucket and GitLab (this one has a screencast).

Copy that URL from the browser, go into the local planets repository, and run this command:

% git remote add origin https://github.com/vlad/planets.git

Make sure to use the URL for your repository rather than Vlad’s: the only difference should be your username instead of vlad.

We can check that the command has worked by running git remote -v:

% git remote -v

origin   https://github.com/vlad/planets.git (push)
origin   https://github.com/vlad/planets.git (fetch)

The name origin is a local nickname for your remote repository. We could use something else if we wanted to, but origin is by far the most common choice.

Once the nickname origin is set up, this command will push the changes from our local repository to the repository on GitHub:

% git push origin master

Counting objects: 9, done.
Delta compression using up to 4 threads.
Compressing objects: 100% (6/6), done.
Writing objects: 100% (9/9), 821 bytes, done.
Total 9 (delta 2), reused 0 (delta 0)
To https://github.com/vlad/planets
 * [new branch]      master -> master
Branch master set up to track remote branch master from origin.

Our local and remote repositories are now in this state:

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 master once the remote has been set up.

We can pull changes from the remote repository to the local one as well:

% git pull origin master

From https://github.com/vlad/planets
 * branch            master     -> 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.

GitHub GUI

Browse to your planets repository on GitHub. Under the Code tab, find and click on the text that says “XX commits” (where “XX” is some number). Hover over, and click on, the three buttons to the right of each commit. What information can you gather/explore from these buttons? How would you get that same information in the shell?

Solution

GitHub Timestamp

Create a remote repository on GitHub. Push the contents of your local repository to the remote. Make changes to your local repository and push these changes. Go to the repo you just created on GitHub and check the timestamps of the files. How does GitHub record times, and why?

Solution

Push vs. Commit

In this lesson, we introduced the git push command. How is git push different from git commit?

Solution

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 http://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

On linux.bath the proxy should be configured to allow you to use git with remote repositories over http so askan demonstrator if you have any issues.

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, 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.

Key Points

• A local Git repository can be connected to one or more remote repositories.
• Use the HTTPS protocol to connect to remote repositories until you have learned how to set up SSH.
• git push copies changes from a local repository to a remote repository.
• git pull copies changes from a remote repository to a local repository.

Previous

Schedule

Next