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My base system is Debian and came with ftp.debian.org in the sources.list file. I have since added the latest Ubuntu repositories to my sources.list file and taken out the original Debian one.

Unfortunately all the packages I installed with the Debian repository that also exist in the Ubuntu repositories do not get replaced with an apt update, upgrade, dist-upgrade or full-upgrade.

So how can I force the reinstallation of currently installed packages from the old and removed repository with ones that exist in the new repositories?

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  • Debian is not Ubuntu, and vice versa. If you want to switch from Debian to Ubuntu, you should re-install your system. – Stephen Kitt Oct 26 '20 at 16:44
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A safer alternative would be to save the output of dpkg --get-selections, reinstall the machine with Ubuntu, and then use dpkg --set-selections to install the same set of packages on Ubuntu.

It's possible to get apt to do what you want. But first a warning: this type of change can easily leave you with a system that won't boot or is broken in other subtle or not-so-subtle ways. You should be fully prepared to either fix difficult problems or do a reinstall and restore data from backups.

You need to create an apt pin for Ubuntu packages with a priority at least 1000. This allows apt to install the Ubuntu version even if it means downgrading. Create /etc/apt/preferences.d/ubuntu with this content:

Package: *
Pin: release o=Ubuntu
Pin-Priority: 1001

You should update /etc/apt/sources.list, install the ubuntu-keyring package manually, and run apt update. (Sounds like you've already done these steps.) Then you can try an apt full-upgrade to move all packages to the Ubuntu versions.

Remove /etc/apt/preferences.d/ubuntu when you're done.

Note that Debian and Ubuntu use different naming for the Linux kernel meta-package, so you'll need to manually uninstall the Debian one (e.g., linux-image-amd64), install the Ubuntu one (e.g., linux-image-generic), and maybe manually remove the Debian linux-image-*-amd64 packages.

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