You have to use drop in units or something in /etc, files in /lib are not supposed to be modified.
** Changed in: apt (Ubuntu) Status: New => Invalid -- You received this bug notification because you are a member of Ubuntu Touch seeded packages, which is subscribed to apt in Ubuntu. https://bugs.launchpad.net/bugs/1708930 Title: update overwrites customized apt-daily.timer Status in apt package in Ubuntu: Invalid Bug description: Ubuntu 16.04.03 LTS apt (1.2.24) I customize /lib/systemd/system/apt-daily.timer on my public facing servers so they only update and reboot once a week, at an earlier time of day, to reduce downtime during a busy part of our day. The update this week overwrote the file with no notice or prompting that it was about to overwrite a customized file. This turned out badly as we had servers rebooting a couple days later at the worst time of the day. To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/apt/+bug/1708930/+subscriptions -- Mailing list: https://launchpad.net/~touch-packages Post to : touch-packages@lists.launchpad.net Unsubscribe : https://launchpad.net/~touch-packages More help : https://help.launchpad.net/ListHelp