Bug#919915: grub2-common: fails to upgrade from 'stretch-backports' - trying to overwrite /etc/kernel/postinst.d/zz-update-grub from grub-cloud-amd64 0.0.4~bpo9+1

[Andreas Beckmann]

Package: grub2-common
Version: 2.02+dfsg1-10
Severity: serious
User: debian-qa at lists.debian.org
Usertags: piuparts
Control: affects -1 + grub-cloud-amd64

Hi,

during a test with piuparts I noticed your package fails to upgrade from
'stretch'.
It installed fine in 'stretch', then the upgrade to 'buster' fails
because it tries to overwrite other packages files without declaring a
Breaks+Replaces relation.

See policy 7.6 at
https://www.debian.org/doc/debian-policy/ch-relationships.html#overwriting-files-and-replacing-packages-replaces

>From the attached log (scroll to the bottom...):

  Unpacking grub2-common (2.02+dfsg1-10) over (2.02~beta3-5+deb9u1) ...
  dpkg: error processing archive /tmp/apt-dpkg-install-lSZYhO/12-grub2-common_2.02+dfsg1-10_amd64.deb (--unpack):
   trying to overwrite '/etc/kernel/postinst.d/zz-update-grub', which is also in package grub-cloud-amd64 0.0.4~bpo9+1
  dpkg-deb: error: paste subprocess was killed by signal (Broken pipe)

Interestingly I could only trigger this error so far on a stretch->stetch-backports->buster
upgrade path. Dependencies seem to be tight enough to prevent this within buster itself.


cheers,

Andreas
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