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今天是 Git 系列课程第二课，上一课我们已经学会在本地创建一个空仓库，痞子衡今天要讲的是如何将本地仓库与远程建立联系。
1. 将本地仓库挂上远程 git remote
本地建好了仓库，我们希望能够挂到远程服务器上，方便与其他人共享。目前最流行的远程 Git 服务器当然是 github，此时你需要在 github 上注册账户并在线创建一个仓库，此处我们输入仓库名为 gittest
点击"Create repository"之后便弹出如下画面，最重要的是我们可以得到一个远程仓库的地址：git@github.com:JayHeng/gittest.git。
有了远程仓库地址，我们便可以开始将本地仓库与远程仓库建立联系：
// 与远程建立连接之前需要保证本地仓库为非空，即至少需要一次本地提交
jay@pc MINGW64 /d/my_project/gittest (master)
$ echo "# gittest" >> README.md
jay@pc MINGW64 /d/my_project/gittest (master)
$ git add README.md
warning: LF will be replaced by CRLF in README.md.
The file will have its original line endings in your working directory.
jay@pc MINGW64 /d/my_project/gittest (master)
$ git commit -m "first commit"
[master (root-commit) 5fe04f8] first commit
1 file changed, 1 insertion(+)
create mode 100644 README.md
// 本地有了提交之后，开始与远程的地址建立联系
jay@pc MINGW64 /d/my_project/gittest (master)
$ git remote add origin git@github.com:JayHeng/gittest.git
// 确认本地与远程的联系
jay@pc MINGW64 /d/my_project/gittest (master)
$ git push -u origin master
The authenticity of host 'github.com (xxx.xx.xxx.xxx)' can't be established.
RSA key fingerprint is SHA256:xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx.
Are you sure you want to continue connecting (yes/no)? yes
Warning: Permanently added 'github.com,xxx.xx.xxx.xxx' (RSA) to the list of known hosts.
git@github.com: Permission denied (publickey).
fatal: Could not read from remote repository.
Please make sure you have the correct access rights
and the repository exists.
很不幸，我们似乎没有与远程建立正确的联系，提示“Permission denied”，这是因为 github 账号没有设置 ssh 公钥信息所致，需要前往 github 网站的"account settings"，依次点击"Setting -> SSH and GPG Keys"->"New SSH key"，将本地的 rsa key（id_rsa.pub 里的字符串）填写进去，下面是生成本地 rsa key 的方法：
// 创建本地 rsa key（如果没有的话，一直 enter/yes；此处痞子衡已经生成过，故直接用之前的 key）
jay@pc MINGW64 /d/my_project/gittest (master)
$ ssh-keygen -t rsa
Generating public/private rsa key pair.
Enter file in which to save the key (/c/Users/jay/.ssh/id_rsa):
/c/Users/jay/.ssh/id_rsa already exists.
Overwrite (y/n)? n
在 github 网站设置好正确 rsa key 之后便可以再次尝试与将本地与远程进行连接：
// 再试一次确认本地与远程的联系
jay@pc MINGW64 /d/my_project/gittest (master)
$ git push -u origin master
Warning: Permanently added the RSA host key for IP address 'xxx.xx.xxx.xxx' to the list of known hosts.
Counting objects: 3, done.
Writing objects: 100% (3/3), 213 bytes | 213.00 KiB/s, done.
Total 3 (delta 0), reused 0 (delta 0)
To github.com:JayHeng/gittest.git
* [new branch] master -> master
Branch 'master' set up to track remote branch 'master' from 'origin'.
好了，大功告成，此时我们已经成功将本地与远程建立了联系，本地分支叫 master，对应的远程分支是 origin。
2. 克隆远程仓库到本地 git clone
Git 是可以远程协作的，这意味着任何人建立的共享远程仓库都可以被复制到任何机器上，只需要知道远程仓库地址即可。
// 将远程 repo 克隆到本地
jay@pc MINGW64 /d/my_project
$ git clone git@github.com:JayHeng/gittest.git
Cloning into 'gittest'...
remote: Counting objects: 3, done.
remote: Total 3 (delta 0), reused 3 (delta 0), pack-reused 0
Receiving objects: 100% (3/3), done.
有了远程共享，再也不用担心本地仓库丢失了，想 clone 就 clone，so easy！
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