Have you ever come across the issue, where you have pushed your code to a central repository but unknowingly old commit also has been pushed which is not required any more.
In general, If you want to revert a last commit:
$ git revert d768b8d6a709ba5524e2cf68915d718b9e9ae0bf
In your last push, you have pushed two commits and imagine second commit now you want to roll back,
$ git revert a768b8d6a709ba5524e2cf68915d718b9e9ae0be
fatal: Commit 137ea95 is a merge but no -m option was given.
You will come across above issue,
To resolve that, we need use -m option with order of a commit. Like below,
$ git revert a768b8d6a709ba5524e2cf68915d718b9e9ae0be - m 2
This will revert second commit which you have made.
Source:
http://gitready.com/intermediate/2009/03/16/rolling-back-changes-with-revert.html