Issue
I'm using Ubuntu and its tomcat9 package. When time comes to upgrading tomcat (sudo apt upgrade tomcat9) what effect does that have on my custom/manual modifications on config files like server.xml?
Does apt-upgrade completely overwrite my custom config changes, does it try to merge them, or something else?
Solution
The files in /etc/tomcat9 are not technically "conffiles" (according to dpkg), but are treated in the same way by the maintainer scripts (cf. ucf(1) manpage).
You'll be offered the usual choice: use the maintainer's version or your version. Later on you can merge them yourself (the rejected version will be saved with a .ucf-new or .ucf-dist extension).
Answered By - Piotr P. Karwasz