In the current documentation for "backup with mongodump", it says

Alternatively, you can shut down a secondary and use mongodump with the data files directly. If you shut down a secondary to capture data with mongodump ensure that the operation can complete before its oplog becomes too stale to continue replicating.

but the offline mongodump was removed in version 3.0. Please see the mongodump documentation in the same version of the docs.

I believe the quoted text should be removed and a note added that this changed in 3.0 and up in the 3.0 and 3.2 versions of the manual.