The issue seems to occur when copying the "/etc/apt/apt.conf.d/10periodic" file using the "cp" command, for reasons unknown. There are no issues found with the filesystem when checked with "fsck", and the "rsync" command works fine.
Temporary solution: (1) Locate the problematic deb package: "/var/cache/apt/archives/update-notifier-common_3.192.1.21_all.deb" (2) After extracting, delete the "10periodic" file and the line corresponding to "10periodic" in "conffiles". (3) Organize the files according to the deb package format, then repackage: sudo dpkg -b update-notifier-common_3.192.1.21_all update-notifier-common_3.192.1.21_all.deb (4) Install the new package with "--force-overwrite", and fix the broken apt. sudo cp update-notifier-common_3.192.1.21_all.deb /var/cache/apt/archives cd /var/cache/apt/archives sudo dpkg -i --force-overwrite update-notifier-common_3.192.1.21_all.deb sudo apt install -f The attached deb package is created using the above method, for Ubuntu 18.04. ** Attachment added: "update-notifier-common_3.192.1.21_all.deb" https://bugs.launchpad.net/ubuntu/+source/update-notifier/+bug/1982051/+attachment/5760721/+files/update-notifier-common_3.192.1.21_all.deb -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/1982051 Title: Unable to install update-notifier-common To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/update-notifier/+bug/1982051/+subscriptions -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs