Rename detection at git log

How can I see all changes for one file ? Including renames/copies ? Currently I don't known how to see them :

> mkdir 1 && cd 1 && git init-db

defaulting to local storage area

> date >> a
> git add a
> git commit -a -m "1"

Committing initial tree c47d83a6544612309aad57519ca831cf62a489d5

> mkdir b
> git mv a b/
> git commit -a -m "2"
> PAGER=cat git log -M -C --pretty=oneline b/a

3b591f7147ee8dbe15fdf456db5730072d41bed8 2

At lastline I would like to see two commits : renaming a -> b/a and creation of a. By the way, how can I see commit message with git log ?

Thanks for help.