We believe that your issue has been closed by the upload of
Version 0.23 of grml-debootstrap from Michael Prokop <mika@grml.org>.
The explanation is attached below

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Hash: SHA1

Format: 1.8
Date: Mon, 24 Nov 2008 23:29:30 +0100
Source: grml-debootstrap
Binary: grml-debootstrap
Architecture: source all
Version: 0.23
Distribution: unstable
Urgency: low
Maintainer: Michael Prokop <mika@grml.org>
Changed-By: Michael Prokop <mika@grml.org>
Description: 
 grml-debootstrap - wrapper around debootstrap for installing plain Debian via grml
Changes: 
 grml-debootstrap (0.23) unstable; urgency=low
 .
   The "hey, rocking - we get patches via git" release.
 .
   * Improve look'n'feel of partition error dialog.
   * Improve documentation regarding installation of bootloader when
     using directories as installation target. Thanks Tong Sun!
     [Closes: issue539]
   * Copy /etc/debootstrap/[s]bin as well to the chroot if they are
     present. Suggestion by Tong Sun - thanks! [Closes: issue540]
   * Apply several patches by Tong Sun (thanks!):
     - allow symlinks when coping existing files to chroot.
     - pre-seed packages using /etc/debootstrap/debconf-selections
       [Closes: issue518]
     - support DEBOOTSTRAP_OPT for passing extra parameters to the
       debootstrap command
     - support KEEP_SRC_LIST to allow user to provide their
       own apt sources.list from /etc/debootstrap/etc/apt/sources.list
     - provide cmdline processing in separate script
     - added the '-d, --confdir=path' option
     - added "--nodebootstrap": Skip debootstrap, only do configuration
       to the target
     - add -v, --verbose: Increase verbosity
     - do not create stage file at finalize()
   * Edit /etc/network/interfaces as well if the file exists already,
     we definitely need at least a loopback interface.
   * Adjust postfix configuration:
     - modify hostname related options in /etc/postfix/main.cf
     - listen on loopback interface by default (thanks for suggestion, gebi)
   * Unify the --bootappend option, it's not --boot_append (thanks for
     the hint, Tong Sun).
   * Support execution of further scripts via options --scripts and
     --chroot-scripts.
   * Drop locales from RECONFIGURE list (thanks for hint, Tong Sun).
     [Closes: issue560]
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 6d6466919938b105b86f30c5365feb5578cef0d8 132572 grml-debootstrap_0.23.tar.gz
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Checksums-Sha256: 
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Files: 
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Oh, I didn't read clearly to understand the correlation between --grub and
--target. Fixed in the doc.

* Tong Sun <bts@bts.grml.org> [20081003 22:32]:

> I invoke grml-debootstrap as:

>  grml-debootstrap --target $os_mnt --grub $os_grb --groot $os_grb

> whereas os_mnt=/mnt/os12 os_grb=hda0,5

> but at the end, I still get the warning

>  Warning: $GROOT is not defined, will not adjust grub configuration therefore.

Well, the bootloader stuff wasn't supposed to work on targets being
directories (but on devices only). Are you interested in working on
that?

regards,
-mika-

I invoke grml-debootstrap as:

 grml-debootstrap --target $os_mnt --grub $os_grb --groot $os_grb

whereas os_mnt=/mnt/os12 os_grb=hda0,5

but at the end, I still get the warning

 Warning: $GROOT is not defined, will not adjust grub configuration therefore.