一、 切换到被copy的分支（master），并且从远端拉取最新版本

$git checkout master

$git pull

二、从当前分支拉copy开发分支

$git checkout -b dev

Switched to a new branch 'dev'

三、 把新建的分支push到远端

$git push origin dev

四、拉取远端分支

$git pull

There is no tracking information for the current branch.

Please specify which branch you want to merge with.

See git-pull(1) for details.

git pull <remote> <branch>

If you wish to set tracking information for this branch you can do so with:

git branch --set-upstream-to=origin/<branch> dev

经过验证，当前的分支并没有和本地分支关联，根据提示进行下一步：

五、关联

$git branch --set-upstream-to=origin/dev

六、 再次拉取 验证

$git pull