github不小心同步覆盖了本地文件

昨天不小心github的commit还没push就同步了，导致本地文件被覆盖，一度以为没救了。 后来得微博 @空非无和 @柳烟堆雪 指点，用git reflog 恢复了文件。

事情是这样的。。。 
我在两个电脑上修改一个项目，A修改文件a，B修改文件b。然后我干了下面这些事，按时间顺序。。。 
1. A上 git commit 
2. A上 git push 
3. B上 git commit 
4. B上 git pull 
然后。。。B上修改的b就被覆盖了。。。

而且git log已经找不到第3步的commit了。

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解决方案： 
执行git reflog

502dd0f HEAD@{0}: pull --progress --rebase --prune origin master  
147b3b5 HEAD@{1}: commit: commit-mark
502dd0f HEAD@{2}: rebase finished: returning to refs/heads/master  

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然后

git reset --hard 502dd0f
git cherry-pick 147b3b5

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就可恢复原来B上的本地文件， 然后push到服务器端：

git push origin master

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但出现：

 ! [rejected]        master -> master (non-fast-forward)
error: failed to push some refs to 'https://github.com/GitUsername/GitProgramName.git'
hint: Updates were rejected because a pushed branch tip is behind its remote
hint: counterpart. Check out this branch and integrate the remote changes
hint: (e.g. 'git pull ...') before pushing again.
hint: See the 'Note about fast-forwards' in 'git push --help' for details.

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可见，线下线上文件出现了冲突。 
解决方法：

1. git pull
2. 如果有冲突，解决冲突
3. git push

但是git pull出现问题：

You are not currently on a branch. Please specify which
branch you want to merge with. See git-pull(1) for details.

    git pull <remote> <branch>

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解决方法：切换到master，再执行git push

git checkout -b temp
git checkout master

from: http://blog.csdn.net/abcjennifer/article/details/45101153