Comment 1 for bug 2058741

Hello Seb. Thank you for your bug report,

Indeed, during installation, curtin apt-config backs up the original ubuntu.sources file before making modifications:

https://github.com/canonical/curtin/blob/master/curtin/commands/apt_config.py#L650

I suggest we either remove it completely or use a different extension. By default on noble, the following extensions should be ignored without warning:

$ apt-config dump | grep -F Dir::Ignore-Files-Silently
Dir::Ignore-Files-Silently "";
Dir::Ignore-Files-Silently:: "~$";
Dir::Ignore-Files-Silently:: "\.disabled$";
Dir::Ignore-Files-Silently:: "\.bak$";
Dir::Ignore-Files-Silently:: "\.dpkg-[a-z]+$";
Dir::Ignore-Files-Silently:: "\.ucf-[a-z]+$";
Dir::Ignore-Files-Silently:: "\.save$";
Dir::Ignore-Files-Silently:: "\.orig$";
Dir::Ignore-Files-Silently:: "\.distUpgrade$";