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Working with multiple remotes¶
NOTE: using bash/git commands is not fully supported on jupyterlite yet (due to single thread/process restriction), and the cells below might error out on the browser (jupyterlite) version of this notebook
Distributed versus centralised¶
Older version control systems (cvs, svn) were "centralised"; the history was kept only on a server, and all commits required an internet.
| Centralised | Distributed |
|---|---|
| Server has history | Every user has full history |
| Your computer has one snapshot | Many local branches |
| To access history, need internet | History always available |
| You commit to remote server | Users synchronise histories |
| cvs, subversion(svn) | git, mercurial (hg), bazaar (bzr) |
With modern distributed systems, we can add a second remote. This might be a personal fork on github:
import os
top_dir = os.getcwd()
git_dir = os.path.join(top_dir, 'learning_git')
working_dir = os.path.join(git_dir, 'git_example')
os.chdir(working_dir)
%%bash
git switch main
git remote add arc git@github.com:UCL-ARC-RSEing-with-Python/github-example.git
git remote -v
We can push to a named remote:
%%writefile Pennines.md
Mountains In the Pennines
========================
* Cross Fell
* Whernside
%%bash
git add Pennines.md
git commit -m "Add Whernside"
%%bash
git push -uf arc main
Referencing remotes¶
You can always refer to commits on a remote like this:
%%bash
git fetch
git log --oneline --left-right arc/main...origin/main
To see the differences between remotes, for example.
To see what files you have changed that aren't updated on a particular remote, for example:
%%bash
git diff --name-only origin/main
When you reference remotes like this, you're working with a cached copy of the last time you interacted with the remote. You can do git fetch to update local data with the remotes without actually pulling. You can also get useful information about whether tracking branches are ahead or behind the remote branches they track:
%%bash
git branch -vv
bare_dir = os.path.join(git_dir, 'bare_repo')
os.chdir(git_dir)
%%bash
mkdir -p bare_repo
cd bare_repo
git init --bare
os.chdir(working_dir)
%%bash
git remote add local_bare ../bare_repo
git push -u local_bare main
%%bash
git remote -v
You can now work with this local repository, just as with any other git server. If you have a colleague on a shared file system, you can use this approach to collaborate through that file system.
Home-made SSH servers¶
Classroom exercise: Try creating a server for yourself using a machine you can SSH to:
ssh <mymachine>
mkdir mygitserver
cd mygitserver
git init --bare
exit
git remote add <somename> ssh://user@host/mygitserver
git push -u <somename> main
SSH keys and GitHub¶
Classroom exercise: If you haven't already, you should set things up so that you don't have to keep typing in your password whenever you interact with GitHub via the command line.
You can do this with an "ssh keypair". You may have created a keypair in the Software Carpentry shell training. Go to the ssh settings page on GitHub and upload your public key by copying the content from your computer. (Probably at .ssh/id_rsa.pub)
If you have difficulties, the instructions for this are on the GitHub website.