Shulou(Shulou.com)06/01 Report--

Git is a free, open source distributed version control system for agile and efficient handling of any small or large project, an open source version control software developed to help manage Linux kernel development.

The GitHub website provides free Git storage for open source projects.

GitLab is an open source project for warehouse management systems. Use Git as a code management tool, and build a web service on this basis.

The main difference between Git and other version control systems is that Git is only concerned with whether the overall file data has changed, while most other systems are only concerned with specific differences in file content. This kind of system (CVS,Subversion,Perforce,Bazaar, etc.) records which files have been updated and what lines have been updated each time. Git takes a snapshot of the changed files and records them in a miniature file system. Each time an update is submitted, it goes through the fingerprint information of all the files and takes a snapshot of the file, and then saves an index that points to the snapshot. To improve performance, Git will not save the file again if there is no change, but will only link to the last saved snapshot. How Git works is shown in the figure below.

Advantages of Git:

Fast processing speed

All operations only need to access local files and resources without connecting to the Internet.

Maintain data integrity at all times

Before saving to Git, all data is calculated by content checksum (checksum), and the result is used as a unique identification and index of the data. If the file becomes incomplete during transfer, or if the disk is corrupted and the file data is missing, Git can detect it immediately. In fact, everything stored in the Git database is indexed by this hash value, not by the file name.

Most operations only add data

Most of the common Git operations simply add data to the database. Because any irreversible operation, such as deleting data, can make it difficult to roll back or reproduce historical versions, in Git, once a snapshot is submitted, there is no need to worry about losing data, especially to get into the habit of regularly pushing it to other warehouses.

Three states of the Git file:

For any file, there are only three states within the Git: submitted (committed), modified (modified), and temporarily saved (staged). Submitted means that the file has been safely saved in the local database; modified means that a file has been modified but has not been submitted for saving; temporarily saved means to put the modified file in the list to be saved the next time it is submitted. From this we can see that when Git manages the project, there are three work areas where files are transferred: the working directory of Git, the temporary storage area, and the local warehouse. We can judge the status from the location of the file: if it is a specific version of the file saved in the Git directory, it belongs to the submitted state; if it has been modified and put into the temporary storage area, it belongs to the temporary storage state; if it has been modified since the last time it was taken out, but has not been put into the temporary storage area, it is the modified state.

Each project has a Git directory (the .git directory if git clone comes out; if git clone-- bare, the new directory itself is the Git directory. Which is where Git holds metadata and object databases This directory is very important, and every time you clone an image repository, you actually copy the data in this directory.

All the files and directories of a certain version are taken out of the project and used to start the follow-up work is called the working directory. These files are actually extracted from the compressed object database in the Git directory, which can then be edited in the working directory.

The so-called temporary storage area is just a simple file, which is usually placed in the Git directory. Sometimes people call this file an index file, but the standard term is still a temporary storage area.

The basic Git workflow is as follows:

Modify some files in the working directory.

Take a snapshot of the modified file and save it to the staging area.

Submit updates and permanently dump snapshots of files saved in the staging area to the Git directory.

Git installation process (CentOS)

1. Check the version number of Git. CentOS installs git version 1.7.X by default, which can be updated to 2.0.5.

# git-version

two。 Install the required software packages

# yum-y install curl-devel expat-devel gettext-devel openssl-devel zlib-devel

# yum-y install gcc perl-ExtUtils-MakeMaker

3. Delete an existing git (do not use the yum remove command as much as possible)

# yum-y remove git

4. Install using the package

# wget httos://www.kerenl.org/pub/software/scm/git/git-2.0.5.tar.gz

# tar zxf git-2.0.5.tar.gz-C / usr/src

# cd / usr/src/git-2.0.5/

# make prefix=/usr/local/git all

# make prefix=/usr/local/git install

# echo "export PATH=$PATH:/usr/local/git/bin" > > / etc/exprofile

# source / etc/exprofile

5. Check the version number of Git again

# git-version

Creation and use of version Library

Version library, also known as warehouse, English name repository, you can simply understand as a directory, this directory all the files can be managed by Git, each file modified, deleted, Git can track, so that at any time you can track history, or at some point in the future can be "restored".

# mkdir / data/git / / Warehouse path

# git init / / change this directory into a warehouse that can be managed by Git through the git init command

Initialize the empty Git version library in / data/git/.git/

# ll-ah / / you can see the hidden .get directory, which is used to track administrative version libraries

Total dosage 12K

Drwxr-xr-x. 3 root root 4.0K March 18 15:53.

Drwxr-xr-x. 3 root root 4.0K March 18 15:53..

Drwxr-xr-x. 7 root root 4.0K March 18 15:53. Git

Because Git is a distributed version control system, every machine must report itself: your name and Email address.

Configuration settings:

# git config-- global user.name "pansy" / / set the name

# git config user.email "pansy@example.com" / / Email address

Note the-global parameter of the git config command, which means that all Git repositories on your machine will use this configuration. Of course, you can also specify a different user name and Email address for a warehouse.

Put the files in the Git warehouse

# cd / data/git / / files should be placed in the warehouse directory or subdirectory

# cat a.txt

This is a txt

# git add a.txt / / add files to the repository

# git add a.txt b.txt / / you can also add multiple files

# git commit-m "add 2 files" / / submission, followed by a description of this submission

[master (root submission) e450576] add 2 files

2 files changed, 2 insertions (+)

Create mode 100644 a.txt

Create mode 100644 b.txt

We have successfully added and submitted an a.txt file, such as modifying the a.txt file

# cat a.txt

This is one txt

# git status / / git status keeps abreast of the current state of the warehouse, which tells us

The master a.txt located in the branch has been modified, but it is not ready to submit the changes, but you cannot see the modified contents.

Changes that have not been temporarily saved for submission:

(use "git add..." Update the content to be submitted)

(use "git checkout--..." Discard changes to the workspace)

Modify: a.txt

Modifications have not been added to submission (using "git add" and / or "git commit-a")

# git diff a.txt / / you can view the modified content

Diff-git a/a.txt b/a.txt

Index 7f38737..3cc29a4 100644

-a/a.txt

+ b/a.txt

@-1 + 1 @ @

-this is a txt

+ this is one txt

Version fallback

# git log / / View history and submit log

Commit bb52f061bae3978b2a72244d23d5133d38e37efe / / commit id

Author: pansy

Date: Sat Mar 18 17:08:53 2017 + 0800

Modify

Commit e450576a118e88aea0953e384b19f3a1abd1ed9f

Author: pansy

Date: Sat Mar 18 16:50:01 2017 + 0800

Add 2 files

Now roll back a.txt to the previous version, the version of "add 2 files"

Git must know which version the current version is. In Git, the current version is represented by HEAD, that is, the latest submitted id, the previous version is head ^, and the previous version is head ^ ^. If you can't write 100 ^ s up to 100, it can be written as HEAD~100.

# git reset-- hard head ^ / / fallback to the previous version

# git log / / View logs

Commit e450576a118e88aea0953e384b19f3a1abd1ed9f

Author: pansy

Date: Sat Mar 18 16:50:01 2017 + 0800

Add 2 files

# git reset-- hard head ^ a.txt / / rollback to the previous version, adding the version library, staging area, and workspace

# git log falls back to the previous version of HEAD.

Commit e450576a118e88aea0953e384b19f3a1abd1ed9f

Author: pansy

Date: Sat Mar 18 16:50:01 2017 + 0800

Add 2 files

If you want to restore that version at this time, use git reset-- hard id

# git reset-- hard bb52f061bae / / id does not need to be written down, it will be found automatically

HEAD is now located in the bb52f06 modification

# git log

Commit bb52f061bae3978b2a72244d23d5133d38e37efe

Author: pansy

Date: Sat Mar 18 17:08:53 2017 + 0800

Modify

Commit e450576a118e88aea0953e384b19f3a1abd1ed9f

Author: pansy

Date: Sat Mar 18 16:50:01 2017 + 0800

Add 2 files

If you can't find commit id,git reflog, record your every command.

# git reflog / / you can view commit id

E450576 HEAD@ {0}: reset: moving to head ^

Bb52f06 HEAD@ {1}: reset: moving to bb52f061bae

E450576 HEAD@ {2}: reset: moving to head ^

Bb52f06 HEAD@ {3}: commit: modify

E450576 HEAD@ {4}: commit (initial): add 2 files

When you change the contents of a file in the workspace and want to discard the changes in the workspace directly, use the command git checkout file.

When you not only change the contents of a file in the workspace, but also add it to the temporary storage area, you want to discard the changes in two steps, the first step is to use the command git reset HEAD file, and the second step is to use git checkout-- file.

When you have submitted inappropriate changes to the version library, you want to undo this submission, as long as you use the above version to back up when you do not push to the remote library.

Delete a file

1. Delete the file completely (need to submit)

# cat b.txt

This is another txt

# git rm b.txt

Rm 'b.txt'

# git status

Located in the branch master

Changes to be submitted:

(use "git reset HEAD..." Withdraw from the temporary storage area)

Delete: b.txt

# git commit-m "Delete b.txt"

[master e380c9f] Delete b.txt

1 file changed, 1 deletion (-)

Delete mode 100644 b.txt

# cat b.txt

Cat: b.txt: there is no such file or directory

two。 Mistakenly delete a file

# git rm b.txt

Rm 'b.txt'

# git reset

Changes to withdraw from the temporary storage area after reset:

Db.txt

# ls

A.txt

# git checkout b.txt

# ls

A.txt b.txt

Remote warehouse

1. Use a website that provides Git warehouse hosting services (GitHub)

GitHub Web site: https://github.com/

(1) Registration (password at least 7 digits and at least one lowercase letter)

(2) choose to pay or free (free here)

(3) use

A.ssh password-free

# ssh-keygen-t rsa-C "pansy@example.com"

Generating public/private rsa key pair.

Enter file in which to save the key (/ root/.ssh/id_rsa):

Enter passphrase (empty for no passphrase):

Enter same passphrase again:

Your identification has been saved in / root/.ssh/id_rsa.

Your public key has been saved in / root/.ssh/id_rsa.pub.

b. Pass the ssh public key to GitHub

# cd ~ / .ssh / / under the user's home directory

# cat id_rsa.pub

Ssh-rsa AAAAB3NzaC1yc2EAAAABIwAAAQEA0y8b25WTVzcZccZCTD8b/4RGAPq6BqbJh0Qe4/o1/IJZqAywusH8FdAL/n0qWE6jhKxHj2g8qgL0GJudyAyyV9Fnbs0XAyjaLeJZ9Y0xS/lVCYcA669gVbZefrsjwxQhpeK4zcuZGkcUJcq8RVA7rRGOIlO+juhGE/B8UqkNrOdCFnoaWTn7CvcGhCeEnXKf4VJoiH6HpYiRl0D2s3qIo2CGtsg/lPd3nsnP73bmf/OsfsUva2CZEMLELWQR193oN8J6VbUkVAqdxRJTi8DlsU/rVxCFfYpxCVqXAh5gvukuGluAZhymV30bw3o+vrQ85gS2XZMq6a02EjxgE97FZw== pansy@example.com

Log in to the website (upload id_rsa.pub to Key and add it) to add a good look.

c. Add a remote library to the website (you need to open the email to agree)

Note: the remote library is public, and the private one needs to pay.

d. Under the local warehouse directory, upload to the gitHub remote library

# cd / data/git

# git remote add origin git@github.com:pansypansy/pansy.repo.git

# git push-u origin master / / the command to upload the local library-u to enter the first time

View

Https://github.com/ user name / remote library name

e. Clone from remote library to local

# git clone git@github.com:pansypansy/two.repo.git / / remote library cloning

Cloning to 'two.repo'...

Remote: Counting objects: 3, done.

Remote: Total 3 (delta 0), reused 0 (delta 0), pack-reused 0

Receiving object: 100% (3thumb 3), complete.

Check the connection. Done.

# cd two.repo/

# ls

README.md

two。 Local git server

GitHub is a remote repository that hosts open source code for free. But for some commercial companies that see source code such as life, they do not want to release the source code and are reluctant to pay GitHub protection fees, so they can only build their own Git server to use as a private warehouse.

(1) install git

# yum-y install git or install it in source code

(2) create users

# useradd git

(3) create certificate login

Collect the public keys of all users who need to log in, which is their own id_rsa.pub file, and import all the public keys into the / home/git/.ssh/authorized_keys file, one line at a time.

(4) initialize Git warehouse

First select a directory as the Git repository, assuming / data/sample.git, and enter the command in the / data directory:

# cd / data

# git init-bare sample.git

# chown-R git:git / data/sample.git/

(5) disable shell login

For security reasons, git users are not allowed to log in to shell, which can be done by editing the / etc/passwd file

Git:x:500:500::/home/git:/bin/bash

Change to:

Git:x:500:500::/home/git:/usr/bin/git-shell

(6) Clone remote warehouse

Git clone git@server:/data/sample.git

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