Git: How to create and apply patch

http://ariejan.net/2009/10/26/how-to-create-and-apply-a-patch-with-git/

To make creating patches easier, there are some common git practices you should follow. It's not necessary, but it will make your life easier.
If you fix a bug or create a new feature – do it in a separate branch!
Let's say you want to create a patch for my imdb gem. You should clone my repository and create a new branch for the fix you have in mind. In this sample we'll do an imaginary fix for empty posters.

git clone git://github.com/ariejan/imdb.git
cd imdb
git checkout -b fix_empty_poster

Now, in the new fix_empty_poster branch you can hack whatever you need to fix. Write tests, update code etc. etc.
When you're satisfied with all you changes, it's time to create your patch. FYI: I'm assuming you made a few commits in the fix_empty_poster branch and did not yet merge it back in to the master branch.
Creating the patch
Okay, I've made some commits, here's the git log for the fix_empty_poster branch:

git log --pretty=oneline -3
* ce30d1f - (fix_empty_poster) Added poster URL as part of cli output (7 minutes ago)
* 5998b80 - Added specs to test empty poster URL behaviour (12 minutes ago)
* aecb8cb - (REL-0.5.0, origin/master, origin/HEAD, master) Prepare release 0.5.0 (4 months ago)

In GitX it would look like this:

Okay, now it's time to go and make a patch! All we really want are the two latest commits, stuff them in a file and send them to someone to apply them. But, since we created a separate branch, we don't have to worry about commits at all!

git format-patch master --stdout > fix_empty_poster.patch

This will create a new file fix_empty_poster.patch with all changes from the current (fix_empty_poster) against master. Normally, git would create a separate patch file for each commit, but that's not what we want. All we need is a single patch file.
Now, you have a patch for the fix you wrote. Send it to the maintainer of the project ...
Applying the patch
... who will apply the patch you just sent! But, before you do that, there are some other steps you should take.
First, take a look at what changes are in the patch. You can do this easily with git apply

git apply --stat fix_empty_poster.patch

Note that this command does not apply the patch, but only shows you the stats about what it'll do. After peeking into the patch file with your favorite editor, you can see what the actual changes are.
Next, you're interested in how troublesome the patch is going to be. Git allows you to test the patch before you actually apply it.

git apply --check fix_empty_poster.patch

If you don't get any errors, the patch can be applied cleanly. Otherwise you may see what trouble you'll run into. To apply the patch, I'll use git am instead of git apply. The reason for this is that git am allows you to sign off an applied patch. This may be useful for later reference.

git am --signoff < fix_empty_poster.patch 
Applying: Added specs to test empty poster URL behaviour
Applying: Added poster URL as part of cli output

Okay, patches were applied cleanly and you're master branch has been updated. Of course, run your tests again to make sure nothing got borked.
In you git log, you'll find that the commit messages contain a "Signed-off-by" tag. This tag will be read by Github and others to provide useful info about how the commit ended up in the code.

imdb_signed_off

Public and Private Keys

https://help.ubuntu.com/community/SSH/OpenSSH/Keys

Generating RSA Keys

The first step involves creating a set of RSA keys for use in authentication.

This should be done on the client.

To create your public and private SSH keys on the command-line:

mkdir ~/.ssh
chmod 700 ~/.ssh
ssh-keygen -t rsa

You will be prompted for a location to save the keys, and a passphrase for the keys. This passphrase will protect your private key while it's stored on the hard drive and be required to use the keys every time you need to login to a key-based system:

Generating public/private rsa key pair.
Enter file in which to save the key (/home/b/.ssh/id_rsa):
Enter passphrase (empty for no passphrase):
Enter same passphrase again:
Your identification has been saved in /home/b/.ssh/id_rsa.
Your public key has been saved in /home/b/.ssh/id_rsa.pub.

Your public key is now available as .ssh/id_rsa.pub in your home folder.

Congratulations! You now have a set of keys. Now it's time to make your systems allow you to login with them