An introduction to the git source control tool that was given at the SouthEast Linux Fest conference in Charlotte, NC USA in 2015

1. An Introduction to Git

2. Disclaimer
My opinions are my own.

3. About Me
Jason Edgecombe (@edgester)
● Linux Administrator in the College of
Engineering at UNC Charlotte
● OpenAFS contributor & buildbot admin
● http://engrmosaic.uncc.edu
● https://github.com/edgester
● http://rampaginggeek.com

4. What is git?
● Distributed version control system
○ Version control system
■ Keeps snapshots of a set of folders and files
■ Let’s you go back in time to any snapshot
○ Distributed
■ All repositories are peers
■ Each repository has full history since last sync
■ Let’s you work without a network connection
■ Authority is determined by choice/convention

5. You should use git because...
● “cp” doesn’t scale (“cp file file.bak5.works”)
● allows for better metadata on snapshots
o description, timestamp, author, committer
● doesn’t clutter folders with copies
● space-efficient, only stores differences
● you don’t need a server to use it locally

6. Common Concepts
● commit - a snapshot in time
o referenced by SHA1 hash of contents
o links to all of its previous commits
o immutable/non-writable!
● branch - a writable variable that refers to a
commit
● tag - a read-only variable that refers to a
commit, with an optional message

7. Common Concepts, Part 2
● repository (a.k.a. “repo”) - A set of folders
that contains the git commit history,
optionally a working folder. Includes
branches & tags
● “remote” - “git remote” - a remote git repo
that is a peer of the current repo
● tracking branch - a local branch that is linked
to a remote branch

8. Concept Hierarchy
● repos contain remotes, branches, tags
● remotes link to tags, branches
● branches and tags refer to commits
● commits refer to files, folders,
parent commits
● repository→remote→branch/tag→commit
→files/folders

9. Common local commands
● Initialization
 git config --global user.name "John Doe"
 git config --global user.email jdoe@example.com
 git init
● Working with files
o Modify files - git add ; git rm ; git mv
● Snapshots
o Save - git commit
o Query - git log; git blame
o Discard changes - git reset; git checkout

10. Common Remote Commands
● Copy a remote repo
o git clone <url/address>
o git checkout origin/master
● Download changes
o git pull --rebase (fetch and rebase)
o git pull
o git fetch
● Upload changes
o git push

11. A Sample Project Workflow
1. “git init” / “git clone” # only once
2. “git checkout -b origin/master
3. “git pull --rebase” # before each session
4. #while working (loop frequently)
a. # edit files
b. “get add .” # to add new files!
c. “git commit .” # commit all modified files
5. “git push” # when work unit is done
6. # goto 2

12. Best Practices
● Jason’s guideline: use “git pull --rebase”
(fetch & rebase) workflow until proficient
● Don’t store code and configuration in the
same repo. (Use .gitignore files if needed)
● DO NOT STORE SECRETS in git!
○ Passwords, ssh keys, etc.
○ May be relaxed for encrypted secrets/isolated repo.

13. Cage Match: Git vs. Subversion
Git: Svn:
Full
history
in all
repos
Only
latest
checko
ut
Branchi
ng is
Branchi
ng is

14. Sources of Confusion
● No pre-defined source of truth for multi-repo
● Many workflows available, all are valid
● Deleted things (git rm) are still in the archive
● History not easily re-written
o “Removed” objects/commits can still persist
o History rewrites can be rejected in receiving repo
● Index (.git/) vs. working folder (./)

15. Git Clients
● Command-line - included in Linux distros
● GUI
o gitk - visualizer, included in distros
o IDE’s: Eclipse, Emacs, Vim
o TortoiseGit (Windows) - terminology mismatch!
 ‘reset’ and ‘revert’ don’t directly map to
command-line git behavior.

16. Demo Time

17. Git Hosting
● Github - https://github.com/
o Free and unlimited repos for open source projects
o Can pay for closed repos
o De facto standard for OSS project collaboration
● BitBucket - https://bitbucket.org/
o Free for a project with up to 5 collaborators

18. Self-Hosted Git
● Free
o Remote ssh server with a git repo
o Gitolite - http://gitolite.com/
o Gitlab CE
● Non-free
o Gitlab - https://about.gitlab.com/
o Atlassian Stash -
https://www.atlassian.com/software/stash

19. More Reading
● “man git-<command>”
o man git-commit
● Git web site
o https://git-scm.com/
● Pro Git book
o https://git-scm.com/book