The Git protocol was created by Linus Torvalds. He also created the original Linux kernel.

Access

repo, https://github.com/gmcmillan100/docs

pages, https://gmcmillan100.github.io/docs/

Test ssh access:

$ ssh -T git@github.com
Hi gmcmillan100! You've successfully authenticated, but GitHub does not provide shell access.

Branch out of sync with master

Do this to bring the lastest changes in master into your local Git branch:

git checkout master git pull git checkout git rebase master

Setup Workflow

Global config:

git config --global user.email "gmcmillan100@gmail.com"
git config --global user.name "Greg McMillan"

Verify the global .gitconfig looks correct:

$ cat .gitconfig
# This is Git's per-user configuration file.
[user]
	name = gmcmillan100
	email = gmcmillan100@gmail.com

Initialize repo and pull down a copy:

mkdir docs
cd docs
git init .
git remote add origin git@github.com:gmcmillan100/docs.git
cat .git/config
git pull git@github.com:gmcmillan100/docs.git master

Push the current branch and set the remote as upstream:

git fetch
git branch --set-upstream-to=origin/master master

Upload some changes:

git add git.md
git commit -m "initial commit"
git pull --rebase
git push

SSH Keys

Main article: https://help.github.com/articles/generating-a-new-ssh-key-and-adding-it-to-the-ssh-agent/#platform-linux

Generate a new ssh key:

$ ssh-keygen -t rsa -b 4096 -C "gmcmillan100@gmail.com"
Generating public/private rsa key pair.

Enter file in which to save the key (/home/greg/.ssh/id_rsa): Enter passphrase (empty for no passphrase): 
Enter same passphrase again: 
Your identification has been saved in /home/greg/.ssh/id_rsa.
Your public key has been saved in /home/greg/.ssh/id_rsa.pub.
The key fingerprint is:
ef:63:96:f2:47:90:76:69:27:ab:62:9b:d9:df:67:ea gmcmillan100@gmail.com
The key's randomart image is:
+--[ RSA 4096]----+
|                 |
|                 |
|           . .   |
|          + = .  |
|        S. + +   |
|         .  o    |
|          .+     |
|        +=* ..  o|
|       .+B++..E+ |
+-----------------+

Display existing key files:

$ ls -al ~/.ssh
total 20
drwx------  2 greg  greg   512 Jan  2 15:27 .
drwxr-xr-x  4 greg  greg   512 Jan  1 07:12 ..
-rw-------  1 greg  greg  3326 Jan  2 15:27 id_rsa
-rw-r--r--  1 greg  greg   748 Jan  2 15:27 id_rsa.pub
-rw-r--r--  1 greg  greg  1014 Jan  2 15:17 known_hosts

Start the ssh-agent and add the new key:

$ eval "$(ssh-agent -s)"
Agent pid 1034

$ ssh-add ~/.ssh/id_rsa
Enter passphrase for /home/greg/.ssh/id_rsa: 
Identity added: /home/greg/.ssh/id_rsa (/home/greg/.ssh/id_rsa)

Display the new public key:

$ cat ~/.ssh/id_rsa.pub 
ssh-rsa AAAAB3NzaC1yc2EAAAADAQABAAACAQDF+17iqUOfTtcjlAEDFBNh23qXqn7WGVaXqKMEMIOtezOrHTsS4TF1vLE0aQDXKjlv1JKi1PBm5ueIr+xe+WTswXRjg5dU2iijkeBLVZKo//7HCXY+W5nNO0wCKMNmnng2JwzhGW28FpwafnuhbHahzL1R8fkYUms4qsYQCoMP+femNr1aWEv9nOs7atpXjugrmhQXwZmuUOkci3pYmOXrrDZxko2EVMaSA03mN48uxQ0ZbPn6L06gzu26cZa2Wip79NmlT/+Ilc8qnjH0MahHpXe1k/fX+3VT9IYMomekOP5jTFuZpNtzrzukSnmkjBABH7Esgo+6TSp3vjOVBm8mEQk4KvUyc8s+POY4jrZr8Z8SRFQAo6XfSs0jPhxe7VIkwIt0oV1jOb0g0x/tudpf/byFWjqmQcFh27MIzf4rsPBt+sP6Tyg59Fn6nqC0UhofuxY3rkLtVnBK6VtiKoPdK1xkSJ4vRi7GzOOMe3txOClR9k0Afdj3Oa9q8GTbXjXc65NsMj33eoHnl/f1O1nHo7gFBaPBDvaSCf16sJ6UwrLy2ZfH0cJuFk9Vfp24Sb8L5o5IL8EoY3ydX1UpXEVtxU4140780mWZKgfThxGjO5xTygLs8BcymkN0ZS+RGrocH7sTf7LIzikY1cGBeBs60BaOs90sxROjPnwpTIXqRQ== gmcmillan100@gmail.com

Test key-account auth

After adding the key to github.com > settings, verify Github can see the key-account mapping from my local host:

$ ssh -T git@github.com
Hi gmcmillan100! You've successfully authenticated, but GitHub does not provide shell access.

Can also use -i for more control:

$ ssh -i ~/.ssh/id_rsa -o IdentityAgent=none -T git@github.com
Hi gmcmillan100! You've successfully authenticated, but GitHub does not provide shell access.

and notice how this key produces a different user response:

$ ssh -i ~/.ssh/gmcmilla_at_linkedin.com_ssh_key -o IdentityAgent=none -T git@github.com
Hi gmcmilla_LinkedIn! You've successfully authenticated, but GitHub does not provide shell access.

Cloning

git clone git@github.com:gmcmillan100/docs.git

Multiple SSH keys for different accounts

Problem. During a git push in my personal docs repo, git was using my work ssh key and user identity. My personal key identity was not being used, resulting in no access.

$ cd /Users/gmcmilla/docs
$ git push
ERROR: Permission to gmcmillan100/docs.git denied to gmcmilla_LinkedIn.
fatal: Could not read from remote repository.

Please make sure you have the correct access rights
and the repository exists.

But outside of git push and the repo, my personal ssh key could authenticate with github.com when the key file is read directly:

$ cd ~
$ ssh -i ~/.ssh/id_rsa -o IdentityAgent=none -T git@github.com
Hi gmcmillan100! You've successfully authenticated, but GitHub does not provide shell access.

ssh -vv revealed that only my work SSH key was being used:

$ ssh -vv -T git@github.com
OpenSSH_9.4p1, LibreSSL 3.3.6
...
debug1: identity file /Users/gmcmilla/.ssh/gmcmilla_at_linkedin.com_ssh_key type 0
debug1: identity file /Users/gmcmilla/.ssh/gmcmilla_at_linkedin.com_ssh_key-cert type -1

and IdentityFile was set to my work ssh key everywhere in ~/.ssh/config:

$ cat ~/.ssh/config
...
Match host github.com user org-132020358,org-132020684,org-132020707,org-127256988,org-132020694,org-127349224
  ProxyCommand none
  IdentityFile %d/.ssh/%u_at_linkedin.com_ssh_key

Solution. Create an alias for my personal ssh key for my personal GitHub repo, so it does not conflict with work’s ssh key.

Article: How do I configure git to use multiple SSH keys for different accounts

  1. Before I do anything, ensure my private id_rsa key is added to the keychain:

     $ ssh-add ~/.ssh/id_rsa
 Enter passphrase for /Users/gmcmilla/.ssh/id_rsa: 
 Identity added: /Users/gmcmilla/.ssh/id_rsa (gmcmillan100@gmail.com)
 $ ssh-add -l
 4096 SHA256:fqqsrkCl6ak0zhG1nAUCt9NYX4yJcqc3Wq1gymcLPpE gmcmillan100@gmail.com (RSA)

  2. Create a custom ssh config file. LinkedIn does not allow me to edit ~/.ssh/config, so all customizations must go in a separate custom file.

     touch ~/.ssh/config.custom
 vi ~/.ssh/config.custom

  3. Add a github alias (named github-personal) that points to my personal SSH key IdentityFile at ~/.ssh/id_rsa:

     Host github-personal
    IdentityFile ~/.ssh/id_rsa
    User git
    HostName github.com
    UseKeychain yes

    The user must be git, and the HostName must be github.com.

  4. Identify the origin setting inside my personal repo.

    To see which remote servers you have configured, run the git remote command. It lists the shortnames of each remote handle you’ve specified. If you’ve cloned your repository, you should at least see origin. That is the default name Git gives to the server you cloned from:

     $ cd /Users/gmcmilla/docs
 $ git remote
 origin

    You can also specify -v, which shows you the URLs that Git has stored for the shortname to be used when reading and writing to that remote:

     $ git remote -v
 origin	git@github.com:gmcmillan100/docs.git (fetch)
 origin	git@github.com:gmcmillan100/docs.git (push)

    In Git, origin is a shorthand name for the remote repository that a project was originally cloned from. More precisely, it is used instead of that original repository’s URL - and thereby makes referencing much easier. Remotes are simply an alias that store the URL of repositories. You can see what URL belongs to each remote by using git remote -v.

  5. Change the remote origin to use the new SSH alias:

     $ git remote set-url "origin" "github-personal:gmcmillan100/docs.git"

    Verify it changed:

     $ git remote -v
 origin	github-personal:gmcmillan100/docs.git (fetch)
 origin	github-personal:gmcmillan100/docs.git (push)

    The next time I git push, the alias will be used (see github-personal):

     $ git push
 Enumerating objects: 5, done.
 Counting objects: 100% (5/5), done.
 Delta compression using up to 16 threads
 Compressing objects: 100% (3/3), done.
 Writing objects: 100% (3/3), 933 bytes | 933.00 KiB/s, done.
 Total 3 (delta 2), reused 0 (delta 0), pack-reused 0
 remote: Resolving deltas: 100% (2/2), completed with 2 local objects.
 To github-personal:gmcmillan100/docs.git
    c1e5cd9..99d1978  master -> master

  6. Troubleshooting no identity and no keychain

    During a git push, I noticed my work permissions reverted and started overriding my personal account again:

     $ git push
 ERROR: Permission to gmcmillan100/docs.git denied to gmcmilla_LinkedIn.
 fatal: Could not read from remote repository.

    There was no personal id_rsa key identity in my keychain. It got lost somehow. Maybe LinkedIn SysOps reset it.

     $ ssh-add -l
 The agent has no identities.

    So I added it back in:

     $ ssh-add ~/.ssh/id_rsa
 Enter passphrase for /Users/gmcmilla/.ssh/id_rsa: 
 Identity added: /Users/gmcmilla/.ssh/id_rsa (gmcmillan100@gmail.com)
 $ ssh-add -l
 4096 SHA256:fqqsrkCl6ak0zhG1nAUCt9NYX4yJcqc3Wq1gymcLPpE gmcmillan100@gmail.com (RSA)

    Then, git push in my docs repo began working again:

     $ cd docs
 $ git push
 Enumerating objects: 7, done.
 Counting objects: 100% (7/7), done.
 Delta compression using up to 16 threads
 Compressing objects: 100% (4/4), done.
 Writing objects: 100% (4/4), 806 bytes | 806.00 KiB/s, done.
 Total 4 (delta 3), reused 0 (delta 0), pack-reused 0
 remote: Resolving deltas: 100% (3/3), completed with 3 local objects.
 To github-personal:gmcmillan100/docs.git
 5b35e52..acac7c6  master -> master

    If it’s still not working, remove the identities and re-add:

     $ ssh-add -D
 All identities removed.
 $ ssh-add -l
 The agent has no identities.
 $ ssh-add ~/.ssh/id_rsa

Resources

GitHub Pages, https://pages.github.com/

Markdown reference, https://en.support.wordpress.com/markdown-quick-reference/