How to list ALL git objects in the database?

Is there a better way of getting a raw list of SHA1s for ALL objects in a repository than:
ls .git/objects/??/\*
and
cat .git/objects/pack/*.idx | git show-index

I know about git rev-list --all but that only lists commit objects that are referenced by .git/refs, and I'm looking for everything, including unreferenced objects that are created by git-hash-object, git-mktree etc.

Try

 git rev-list --objects --all

Edit Josh made a good point:

 git rev-list --objects -g --no-walk --all

list objects reachable from the ref-logs.

To see all objects in unreachable commits as well:

 git rev-list --objects --no-walk \
      $(git fsck --unreachable |
        grep '^unreachable commit' |
        cut -d' ' -f3)

Putting it all together, to really get all objects in the output format of rev-list --objects, you need something like

{
    git rev-list --objects --all
    git rev-list --objects -g --no-walk --all
    git rev-list --objects --no-walk \
        $(git fsck --unreachable |
          grep '^unreachable commit' |
          cut -d' ' -f3)
} | sort | uniq

To sort the output in slightly more useful way (by path for tree/blobs, commits first) use an additional | sort -k2 which will group all different blobs (revisions) for identical paths.

I don’t know since when this option exists but you can

git cat-file --batch-check --batch-all-objects

This gives you, according to the man page,

all objects in the repository and any alternate object stores (not just reachable objects)

(emphasis mine).

By default this yields the object type and it’s size together with each hash but you can easily remove this information, e.g. with

git cat-file --batch-check --batch-all-objects | cut -d' ' -f1

or by giving a custom format to --batch-check.

Edit: If you don't care about the order you can (since Git 2.19) add the flag --unordered to speed things up. See VonC's answer for more details.