Looks like on http://test.docs.10gen.cc/master/release-notes/2.6-upgrade/ in the "Upgrade Procedure" section the second code snippit contains the --shutdown flag even though this is not wanted/needed.

Additionally, it might be useful to specify to the reader which mongod binary they are to use to preform these operations. I was confused about whether to use the 2.4 binary (that I am replacing) or the 2.6 binary (that I am putting in) for the shutdown command. Maybe it does not matter, but I was concerned about it personally