git 把远程分支拿到本地，并建立关联关系track

http://www.open-open.com/lib/view/open1328069889514.html

从远程分支 checkout 出来的本地分支，称为_跟踪分支(tracking branch)_。跟踪分支是一种和远程分支有直接联系的本地分支。在跟踪分支里输入git push，Git 会自行推断应该向哪个服务器的哪个分支推送数据。反过来，在这些分支里运行git pull 会获取所有远程索引，并把它们的数据都合并到本地分支中来。

在克隆仓库时，Git 通常会自动创建一个名为 master 的分支来跟踪 origin/master。这正是git push 和 git pull 一开始就能正常工作的原因。当然，你可以随心所欲地设定为其它跟踪分支，比如origin 上除了 master 之外的其它分支。刚才我们已经看到了这样的一个例子：git checkout -b [分支名] [远程名]/[分支名]。

shuohailhl@SHUOHAILHL-PC /f/ggg/jingwei (master)
$ git checkout --track origin/br-2.1.2.1
Branch br-2.1.2.1 set up to track remote branch br-2.1.2.1 from origin.
Switched to a new branch 'br-2.1.2.1'

shuohailhl@SHUOHAILHL-PC /f/ggg/jingwei (br-2.1.2.1)
$ git status
# On branch br-2.1.2.1
nothing to commit, working directory clean

shuohailhl@SHUOHAILHL-PC /f/ggg/jingwei (br-2.1.2.1)
$ git br
* br-2.1.2.1
  br-2.1.2.2
  master

 删掉刚才track的分支

shuohailhl@SHUOHAILHL-PC /f/ggg/jingwei (master)
$ git br
  br-2.1.2.1
  br-2.1.2.2
* master

shuohailhl@SHUOHAILHL-PC /f/ggg/jingwei (master)
$ git status
# On branch master
nothing to commit, working directory clean

shuohailhl@SHUOHAILHL-PC /f/ggg/jingwei (master)
$ git branch -d br-2.1.2.1
warning: deleting branch 'br-2.1.2.1' that has been merged to
         'refs/remotes/origin/br-2.1.2.1', but not yet merged to HEAD.
Deleted branch br-2.1.2.1 (was cec094b).

shuohailhl@SHUOHAILHL-PC /f/ggg/jingwei (master)
$ git br -v
  br-2.1.2.2 1dfeab3 [behind 9] 升级META客户端2.1.4.4
* master     89700a3 optimize upload file

 使用checkout命令，创建新的分支 br-2.1.2.1，跟踪远程的origin/br-2.1.2.1

shuohailhl@SHUOHAILHL-PC /f/ggg/jingwei (master)
$ <span style="color:#ff0000;">git checkout -b br-2.1.1.1  origin/br-2.1.2.1</span>
Branch br-2.1.1.1 set up to track remote branch br-2.1.2.1 from origin.
Switched to a new branch 'br-2.1.1.1'

shuohailhl@SHUOHAILHL-PC /f/ggg/jingwei (br-2.1.1.1)
$ git status
# On branch br-2.1.1.1
nothing to commit, working directory clean

shuohailhl@SHUOHAILHL-PC /f/ggg/jingwei (br-2.1.1.1)

$ git branch -a
* br-2.1.1.1
  br-2.1.2.2
  master
  remotes/origin/HEAD -> origin/master
  remotes/origin/br-2.1.2.1
  remotes/origin/br-2.1.2.2
  remotes/origin/br-2.1.3
  remotes/origin/master