fatal: ambiguous argument 'HEAD': unknown revision or path not in the working tree.

[Thomas Glanzmann]

Hello,

(s017241) [/usr/src/linux-2.6] git checkout v2.6.20
warning: You appear to be on a branch yet to be born.
warning: Forcing checkout of v2.6.20.
fatal: ambiguous argument 'HEAD': unknown revision or path not in the working tree.
Use '--' to separate paths from revisions
Cannot detach HEAD

(s017241) [/usr/src/linux-2.6] git version
git version 1.5.2.1

what is going wrong here?

Thomas

[Junio C Hamano]

Post by Thomas Glanzmann
Hello,
(s017241) [/usr/src/linux-2.6] git checkout v2.6.20
warning: You appear to be on a branch yet to be born.
warning: Forcing checkout of v2.6.20.
fatal: ambiguous argument 'HEAD': unknown revision or path not in the working tree.
Use '--' to separate paths from revisions
Cannot detach HEAD
(s017241) [/usr/src/linux-2.6] git version
git version 1.5.2.1
what is going wrong here?

Perhaps repository was set up in an unusual way by hand
(i.e. not by a clone), such that:

1. you have HEAD pointing at a branch (e.g. 'refs/heads/master'),
2. which does _not_ exist yet (i.e. no 'refs/heads/master'),
3. yet you have a tag that you can try to detach your HEAD to (e.g. v2.6.20).

... well that was my initial guess, but even after setting up such a
funny repository by hand, I cannot seem to reproduce it.

[Thomas Glanzmann]

Hello Junio,

Post by Junio C Hamano
... well that was my initial guess, but even after setting up such a
funny repository by hand, I cannot seem to reproduce it.

This was on a fresh clone. What I did was:

(s017241) [/usr/src] git clone 131.188.30.102:/scratch/tg/linux-2.6/
Initialized empty Git repository in /usr/src/linux-2.6/.git/
remote: Generating pack...
remote: Done counting 496189 objects.
remote: Deltifying 496189 objects...
remote: 100% (496189/496189) done
Indexing 496189 objects...
remote: Total 496189 (delta 401610), reused 496189 (delta 401610)
100% (496189/496189) done
Resolving 401610 deltas...
100% (401610/401610) donedone
fatal: Not a valid object name HEAD

I see it. Last line. I tried to clone from a repository which itself had a
detached HEAD. Could that be the problem?

Thomas

[Junio C Hamano]

Post by Thomas Glanzmann
I see it. Last line. I tried to clone from a repository which itself had a
detached HEAD. Could that be the problem?

Ah, our mails crossed.

There is no reason to forbid cloning of a repository whose HEAD
is detached, but detached HEAD is a relatively recent invention,
and I would not be surprised if that was indeed the breakage,
nor nobody has hit this so far.

It's sufficiently late here so I do not think I would be able to
take a look at it tonight, though. Sorry.

Just in case you need unblocking (although I think you know how
already), you should be able to continue with:

$ git rev-parse v2.6.20^0 >.git/HEAD
$ git read-tree HEAD
$ git checkout-index -f -q -u -a

That would give you a normal detached state at v2.6.20; you
should be able to come back to your branches with usual "git
checkout".

[Thomas Glanzmann]

Hello Junio,
sleep well! And if you want to reproduce it yourself we can e-mail
tomorrow or whenever you like.

Thanks,
Thomas

[Junio C Hamano]

Post by Junio C Hamano
Perhaps repository was set up in an unusual way by hand
1. you have HEAD pointing at a branch (e.g. 'refs/heads/master'),
2. which does _not_ exist yet (i.e. no 'refs/heads/master'),
3. yet you have a tag that you can try to detach your HEAD to (e.g. v2.6.20).
... well that was my initial guess, but even after setting up such a
funny repository by hand, I cannot seem to reproduce it.

Actually, that turns out to be the reason for 'maint' releases,
although it works on 'master' (hence will be in 1.5.3 later).

How did you get your repository into such a state to begin with?

[carbonated beverage]

Post by Junio C Hamano
How did you get your repository into such a state to begin with?

It's kinda odd to see this thread, as I hit this issue today, as well.

If you need another test case, the cvsps git repo shows this too:

ramune/lycaeum:git: git clone http://ydirson.free.fr/soft/git/cvsps.git
<snip checkout messages>
ramune/lycaeum:git: cd cvsps
ramune/lycaeum:cvsps: ls
ramune/lycaeum:cvsps: git checkout -f
warning: You appear to be on a branch yet to be born.
warning: Forcing checkout of HEAD.
fatal: just how do you expect me to merge 0 trees?
ramune/lycaeum:cvsps: cat .git/HEAD
ref: refs/heads/master
ramune/lycaeum:cvsps: ls .git/refs/head/master
ls: .git/refs/head/master: No such file or directory

-- DN
Daniel