git:Please enter a commit message to explain why this merge is necessary

Question description：

I am using git. I did a pull from a remote repo and got an error message:"please enter a commit message to explain why this merge is necessary,especially if it merges
an updated upstream into a topic branch."

scheme  1：

I try to type a message and press enter but nothing happens.

How do I tell git/terminal I am done typing in my message? I am using terminal on OS X.

It's not a Git error message, it's the editor as git uses your default editor.

To solve this:

press "i"

write your merge message

按照提示：

输入ctrl + x

输入 "y"

then press enter

scheme  2：

Actually it's not an error! It means you should enter some message to mark this merge. My OS is Ubuntu 14.04.If you use the same OS ,you just need to do this as follows:

type some message

"Ctrl+C+O"

type the file name(such as "Merge_feature01") and press Enter

"Ctrl+X" to exit

Now if you go to .git and you will find the file "Merge_feature01", that's the merge log actually.