Control: reassign -1 dpkg On Tue, Aug 27, 2019 at 05:34:05PM +0100, Mark Hindley wrote: > Package: apt > Version: 1.8.3 > Severity: important > > Dear apt maintainers, > > This report is a result of my investigation of #934491 which shows that when > trying to migrate a sid install from systemd to sysvinit and elogind by the > most > obvious route it is possible to break the system in a way that is difficult to > recover with the fairly simple command: > > apt install libpam-elogind sysvinit-core > > I think the root cause of the issue is the way apt invokes dpkg when forcing > removals which is not sufficiently responsive to errors. > > In this case apt's dpkg commands are: > > echo 'libpam-systemd:amd64 deinstall' | /usr/bin/dpkg --set-selections > echo 'systemd-sysv:amd64 deinstall' | /usr/bin/dpkg --set-selections > echo 'systemd:amd64 deinstall' | /usr/bin/dpkg --set-selections > echo 'libsystemd0:amd64 deinstall' | /usr/bin/dpkg --set-selections > /usr/bin/dpkg --status-fd 18 --no-triggers --force-depends --remove > libpam-systemd:amd64 > /usr/bin/dpkg --status-fd 18 --no-triggers --unpack --auto-deconfigure > /var/cache/apt/archives/libpam-elogind_241.3-1+debian1_amd64.deb > /usr/bin/dpkg --status-fd 18 --no-triggers --force-depends --remove > systemd-sysv:amd64 > /usr/bin/dpkg --status-fd 18 --no-triggers --unpack --auto-deconfigure > /var/cache/apt/archives/sysvinit-core_2.96~beta-1_amd64.deb > /usr/bin/dpkg --status-fd 18 --no-triggers --force-depends --remove > systemd:amd64 libsystemd0:amd64 > ^^^ The line above causes the problem ^^^ > /usr/bin/dpkg --status-fd 18 --no-triggers --unpack --auto-deconfigure > /var/cache/apt/archives/libelogind0_241.3-1+debian1_amd64.deb > /usr/bin/dpkg --status-fd 18 --no-triggers --configure libelogind0:amd64 > /usr/bin/dpkg --status-fd 18 --no-triggers --unpack --auto-deconfigure > /var/cache/apt/archives/elogind_241.3-1+debian1_amd64.deb > /usr/bin/dpkg --status-fd 18 --configure --pending > > The problem is caused by the invocation forcing the removal of systemd and > libsystemd0. If systemd is pid 1 then its prerm will fail to prevent > removal. However, dpkg still continues to remove libsystemd0 as requested > *before* exiting and signalling an error. apt then stops in response to the > dpkg > error. The system is then broken as there is no libsystemd.so.0 installed > which > apt itself requires. > > My solution is to invoke dpkg with --abort-after=1. The command line > > apt install -o DPkg::Options::="--abort-after=1" install libpam-elogind > sysvinit-core > > no longer breaks a sid systemd system. This means that dpkg exits immediately > after the systemd prerm fails and libsystemd0 remains installed. The > dependencies can then be fixed with apt. > > I suggest that --abort-after=1 should be apt's default when forcing package > removal.
APT is the wrong place for that. We're trying to move to a future where we only tell dpkg all the actions to do and then run a single dpkg, so adding hacks like that feels counter-intuitive. If we agree that this is a good thing to do, dpkg should do it. -- debian developer - deb.li/jak | jak-linux.org - free software dev ubuntu core developer i speak de, en
