This also happened to me when upgrading from 17.10 to 18.04 here's the relevant bit of the upgrade log files:
main.log: 2018-01-05 15:22:34,603 DEBUG failed to SystemUnLock() (E:Not locked) 2018-01-05 15:38:49,081 ERROR got an error from dpkg for pkg: 'systemd': 'triggers looping, abandoned' 2018-01-05 15:38:49,081 DEBUG running apport_pkgfailure() systemd: triggers looping, abandoned 2018-01-05 15:40:02,214 ERROR Exception during pm.DoInstall() Traceback (most recent call last): File "/tmp/ubuntu-release-upgrader-1fsoxbon/DistUpgrade/DistUpgradeView.py", line 218, in run res = pm.do_install(self.writefd) apt_pkg.Error: E:Sub-process /usr/bin/dpkg exited unexpectedly 2018-01-05 15:40:02,265 ERROR SystemError from cache.commit(): installArchives() failed 2018-01-05 15:40:02,265 ERROR found exception: 'E:Sub-process /usr/bin/dpkg exited unexpectedly' apt-term.log: Setting up gstreamer1.0-plugins-bad:amd64 (1.12.4-2ubuntu1) ...^M dpkg: ../../src/packages.c:245: process_queue: Assertion `dependtry <= 4' failed.^M ** Tags added: bionic rls-bb-incoming -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/1512322 Title: dpkg assert failure: dpkg: ../../src/packages.c:245: process_queue: To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/dpkg/+bug/1512322/+subscriptions -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs