79 lines
3.4 KiB
Bash
Executable file
79 lines
3.4 KiB
Bash
Executable file
#!/bin/sh
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#
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# mmdebstrap does have a --merged-usr option but only as a no-op for
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# debootstrap compatibility
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#
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# Using this hook script, you can emulate what debootstrap does to set up
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# merged /usr via directory symlinks, even using the exact same shell function
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# that debootstrap uses by running mmdebstrap with:
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#
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# --setup-hook=/usr/share/mmdebstrap/hooks/merged-usr/setup00.sh
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#
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# Alternatively, you can setup merged-/usr by installing the usrmerge package:
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#
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# --include=usrmerge
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#
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# mmdebstrap will not include this functionality via a --merged-usr option
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# because there are many reasons against implementing merged-/usr that way:
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#
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# https://wiki.debian.org/Teams/Dpkg/MergedUsr
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# https://wiki.debian.org/Teams/Dpkg/FAQ#Q:_Does_dpkg_support_merged-.2Fusr-via-aliased-dirs.3F
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# https://lists.debian.org/20190219044924.GB21901@gaara.hadrons.org
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# https://lists.debian.org/YAkLOMIocggdprSQ@thunder.hadrons.org
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# https://lists.debian.org/20181223030614.GA8788@gaara.hadrons.org
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#
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# In addition, the merged-/usr-via-aliased-dirs approach violates an important
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# principle of component based software engineering one of the core design
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# ideas/goals of mmdebstrap: All the information to create a chroot of a Debian
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# based distribution should be included in its packages and their metadata.
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# Using directory symlinks as used by debootstrap contradicts this principle.
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# The information whether a distribution uses this approach to merged-/usr or
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# not is not anymore contained in its packages but in a tool from the outside.
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#
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# Example real world problem: I'm using debbisect to bisect Debian unstable
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# between 2015 and today. For which snapshot.d.o timestamp should a merged-/usr
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# chroot be created and for which ones not?
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#
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# The problem is not the idea of merged-/usr but the problem is the way how it
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# got implemented in debootstrap via directory symlinks. That way of rolling
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# out merged-/usr is bad from the dpkg point-of-view and completely opposite of
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# the vision with which in mind I wrote mmdebstrap.
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set -eu
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if [ "${MMDEBSTRAP_VERBOSITY:-1}" -ge 3 ]; then
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set -x
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fi
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TARGET="$1"
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# now install an empty "usr-is-merged" package to avoid installing the
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# usrmerge package on this system even after init-system-helpers starts
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# depending on "usrmerge | usr-is-merged".
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#
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# This package will not end up in the final chroot because the essential
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# hook replaces it with the actual usr-is-merged package from src:usrmerge.
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tmpdir=$(mktemp --directory --tmpdir="$TARGET/tmp")
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mkdir -p "$tmpdir/usr-is-merged/DEBIAN"
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cat << END > "$tmpdir/usr-is-merged/DEBIAN/control"
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Package: usr-is-merged
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Priority: optional
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Section: oldlibs
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Maintainer: Johannes Schauer Marin Rodrigues <josch@debian.org>
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Architecture: all
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Multi-Arch: foreign
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Source: mmdebstrap-dummy-usr-is-merged
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Version: 1
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Description: dummy package created by mmdebstrap merged-usr setup hook
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This package was generated and installed by the mmdebstrap merged-usr
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setup hook at /usr/share/mmdebstrap/hooks/merged-usr.
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.
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If this package is installed in the final chroot, then this is a bug
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in mmdebstrap. Please report: https://gitlab.mister-muffin.de/josch/mmdebstrap
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END
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dpkg-deb --build "$tmpdir/usr-is-merged" "$tmpdir/usr-is-merged.deb"
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dpkg --root="$TARGET" --log="$TARGET/var/log/dpkg.log" --install "$tmpdir/usr-is-merged.deb"
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rm "$tmpdir/usr-is-merged.deb" "$tmpdir/usr-is-merged/DEBIAN/control"
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rmdir "$tmpdir/usr-is-merged/DEBIAN" "$tmpdir/usr-is-merged" "$tmpdir"
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