add mmdebstrap as alternative to (c)debootstrap

[adrelanos]

#120

[mika]

Thanks, though I think we should also improve the code to actually fall back to usage of mmdebstrap if the default (debootstrap) isn't available. (I'd also like to get us to using mmdebstrap as the new default BTW :))

[adrelanos]

Oh. It crossed my mind. But I was too shy to suggest mmdebstrap by default. :)

I thought with the goal of backwards compatibility as expressed in #211 (comment) I thought that might be hard.

#211 also looks easy to do except when attempting to keep backwards compatibility.

[mika]

Oh. It crossed my mind. But I was too shy to suggest mmdebstrap by default. :)

I thought with the goal of backwards compatibility as expressed in #211 (comment) I thought that might be hard.

Actually it shouldn't be too hard to get this, even backwards compatible: one could run DEBOOTSTRAP=mmdebstrap ... for all the supported Debian releases and see whether it would break for anything. Even if it does break for older Debian releases, we could start enabling mmdebstrap for only more recent Debian releases? Or if necessary, also check that mmdebstrap is available with a minimum version and fall back to debootstrap else, if that should be relevant.

#211 also looks easy to do except when attempting to keep backwards compatibility.

I just briefly checked, jessie doesn't seem to provide zstd yet, but it's available starting with stretch. (And runny wheezy isn't even easy any more with nowadays kernels due to vsyscall=emulate needs). I'd tend to say, whoever needs to run something older than stretch should also use an older version of grml-debootstrap, and we can agree to consider stretch as the oldest support release from within grml-debootstrap then.