How to fix dpkg: warning: cannot remove non-foreign architecture 'amd64' in APT

Run dpkg --print-architecture to see your system's native architecture. This is the one you cannot remove.

dpkg --print-architecture

On most modern 64-bit systems, this will output amd64. This is your native architecture and cannot be removed.

If you want to remove an architecture, first check which foreign architectures have been added to your system:

dpkg --print-foreign-architectures

If the output is empty, no foreign architectures have been added. Only architectures listed here can be removed.

In a multiarch setup:
- Native architecture: The CPU architecture of your hardware (e.g., amd64). Listed by dpkg --print-architecture. This cannot be removed.
- Foreign architectures: Additional architectures added to support multiarch (e.g., i386 on amd64). Listed by dpkg --print-foreign-architectures. These can be added and removed.

Common foreign architectures include i386 (32-bit) on amd64 (64-bit) systems, or arm64 on amd64 systems.

To remove a foreign architecture (not your native one), use:

sudo dpkg --remove-architecture i386

Before doing this, ensure no packages of that architecture are installed. You may need to uninstall them first:

sudo apt-get purge ".*:i386"
sudo dpkg --remove-architecture i386

Note: Replace i386 with the actual foreign architecture you want to remove.