You are not currently on a branch, so I cannot use any
症状：有一次pull的时候又出现冲突，这回用“git reset --hard FETCH_HEAD”方法都不行了，出现：
$ git pull
You are not currently on a branch, so I cannot use any
'branch.<branchname>.merge' in your configuration file.
Please specify which remote branch you want to use on the command
line and try again (e.g. 'git pull <repository> <refspec>').
See git-pull(1) for details.
解决方法：
首先git checkout -b temp
其次git checkout master
即可恢复到master repository的状态，然后就可以pull了