Remotes in GitLab

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 GitLab, then click on the icon New project to create a new repository called planets_??. Replace ?? with your own username, vlad in my case. We chose it this way to emphasize the difference with our local planets folder. The convenience of it will be apparent very soon. Meanwhile let’s create the repo:

Name your repository (planets_vlad in my case) and then click New project:

Have a look to the different Visibility Levels, they will allow you to tune access to the data stored in GitLab.

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

This effectively does the following on GitLab’s servers:

$ mkdir planets_vlad
$ cd planets_vlad
$ git init

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

The next step is to connect the two repositories. We do this by making the GitLab repository a remote for the local repository. The home page of the repository on GitLab includes the string we need to identify it:

If not already set, click on the ‘HTTPS’ link to change the protocol from SSH to HTTPS.

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://gitlab.ift.uam-csic.es/vlad/planets_vlad.git

Make sure to use the URL for your repository rather than SCWtest’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://gitlab.ift.uam-csic.es/vlad/planets_vlad.git (push)
origin   https://gitlab.ift.uam-csic.es/vlad/planets_vlad.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, let’s push changes from our local repository to the repository on GitLab. First check that you are up to date in your local repo:

$ git status

On branch master
nothing to commit, working tree clean

Then, this command will push your changes from our local repository to the repository on GitLab:

$ 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://gitlab.ift.uam-csic.es/vlad/planets_vlad
 * [new branch]      master -> master
Branch master set up to track remote branch master from origin.

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

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.

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://gitlab.ift.uam-csic.es/vlad/planets_vlad
 * 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 GitLab, though, this command would download them to our local repository.

GitLab GUI

Browse to your planets_vlad repository on GitLab. In the home or Details tab, find and click on the text that say “Commits(XX)” (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

When you click on the button with the commit ID, you’ll see all of the changes that were made in that particular commit. Green shaded lines indicate additions and red ones removals. In the shell we can do the same thing with git diff. In particular, git diff ID1..ID2 where ID1 and ID2 are commit identifiers (e.g. git diff a3bf1e5..041e637) will show the differences between those two commits.

The middle button (with the picture of a clipboard) copies the full identifier of the commit to the clipboard. In the shell, git log will show you the full commit identifier for each commit.

The right-most button lets you view all of the files in the repository at the time of that commit. To do this in the shell, we’d need to checkout the repository at that particular time. We can do this with git checkout ID where ID is the identifier of the commit we want to look at. If we do this, we need to remember to put the repository back to the right state afterwards!

GitLab Timestamp

Create a remote repository on GitLab. 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 GitLab and check the timestamps of the files. How does GitLab record times, and why?

Solution

Github displays timestamps in a human readable relative format (i.e. “22 hours ago” or “three weeks ago”). However, if you hover over the timestamp, you can see the exact time at which the last change to the file occurred.

Push vs. Commit

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

Solution

When we push changes, we’re interacting with a remote repository to update it with the changes we’ve made locally (often this corresponds to sharing the changes we’ve made with others). Commit only updates your local repository.

Fixing Remote Settings

It happens quite often in practice that you made a typo in the remote URL. This exercice is about how to fix this kind of issues. First start by adding a remote with an invalid URL:

git remote add broken https://gitlab.ift.uam-csic.es/this/url/is/invalid

Do you get an error when adding the remote? Can you think of a command that would make it obvious that your remote URL was not valid? Can you figure out how to fix the URL (tip: use git remote -h)? Don’t forget to clean up and remove this remote once you are done with this exercise.

Solution

We don’t see any error message when we add the remote (adding the remote tells git about it, but doesn’t try to use it yet). As soon as we try to use git push we’ll see an error message. The command git remote set-url allows us to change the remote’s URL to fix it.

GitLab README files

In this section we learned about creating a remote repository on GitLab. Sometimes it is useful to let others know what is your repo about by means of a introduction or brief description of the project. This is done by making a special Markdown file README.md. Create this file in your local repo writing a brief description of your project in it. Push it to GitLab afterwards. What do you see when browsing your GitLab repo?

Solution

You see a nice preview of the file at the frontpage of your GitLab repository. Try to enhance the look by using Markdown

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.