How to fix E: Unable to locate package package:i386 in APT

First, enable support for 32-bit packages using dpkg:

sudo dpkg --add-architecture i386

This command registers i386 as an additional architecture that apt should support. You can verify it worked by checking:

dpkg --print-foreign-architectures

You should see "i386" listed in the output.

After enabling the architecture, rebuild the apt package cache:

sudo apt update

This is critical because apt needs to refresh its local cache to recognize i386 packages from all enabled repositories. Without this step, apt will not find the newly available packages.

Some repositories may be restricted to amd64 only. Check your sources:

cat /etc/apt/sources.list
ls /etc/apt/sources.list.d/

If you see entries like deb [arch=amd64], you need to modify them to include i386. Edit the file:

sudo nano /etc/apt/sources.list

Change lines like:

deb [arch=amd64] http://example.com/ubuntu focal main

To:

deb [arch=amd64,i386] http://example.com/ubuntu focal main

Or remove the architecture restriction entirely:

deb http://example.com/ubuntu focal main

Save and run sudo apt update again.

Now you can install the 32-bit package using the :i386 suffix:

sudo apt install package-name:i386

For example, if you were trying to install libc6 for 32-bit:

sudo apt install libc6:i386

You may see a message about installing both amd64 and i386 versions of certain dependencies, which is normal and expected.