APT - Unable to locate package (aspnetcore/dotnet runtime, Ubuntu)

Question

I'm trying to install the aspnetcore-runtime-3.1 package, I have added the microsoft package signing key with

wget https://packages.microsoft.com/config/ubuntu/20.04/packages-microsoft-prod.deb -O packages-microsoft-prod.deb
sudo dpkg -i packages-microsoft-prod.deb

However, sudo apt install aspnetcore-runtime-3.1 gives the error:

Reading package lists... Done
Building dependency tree
Reading state information... Done
E: Unable to locate package aspnetcore-runtime-3.1

Searching for the package with apt search shows that the package does exist:

$ sudo apt search aspnetcore
Sorting... Done
Full Text Search... Done
aspnetcore-runtime-2.1/focal 2.1.20-1 amd64
  Microsoft ASP.NET Core 2.1.20 Shared Framework

aspnetcore-runtime-3.1/focal 3.1.6-1 amd64
  Shared Framework for hosting of Microsoft ASP.NET Core applications. It is open source, cross-platform and is supported by Microsoft. We hope you enjoy using it! If you do, please consider joining the active community of developers that are contributing to the project on GitHub (https://github.com/aspnet/AspNetCore). We happily accept issues and PRs.

aspnetcore-targeting-pack-3.1/focal 3.1.3-1 amd64
  Shared Framework for hosting of Microsoft ASP.NET Core applications. It is open source, cross-platform and is supported by Microsoft. We hope you enjoy using it! If you do, please consider joining the active community of developers that are contributing to the project on GitHub (https://github.com/aspnet/AspNetCore). We happily accept issues and PRs

I've tried the troubleshooting steps listed on the Microsoft docs:

sudo dpkg --purge packages-microsoft-prod && sudo dpkg -i packages-microsoft-prod.deb
sudo apt-get update
sudo apt-get install aspnetcore-runtime-3.1

and

sudo apt-get install -y gpg
wget -O - https://packages.microsoft.com/keys/microsoft.asc | gpg --dearmor -o microsoft.asc.gpg
sudo mv microsoft.asc.gpg /etc/apt/trusted.gpg.d/
wget https://packages.microsoft.com/config/ubuntu/20.04/prod.list
sudo mv prod.list /etc/apt/sources.list.d/microsoft-prod.list
sudo chown root:root /etc/apt/trusted.gpg.d/microsoft.asc.gpg
sudo chown root:root /etc/apt/sources.list.d/microsoft-prod.list
sudo apt-get update; \
  sudo apt-get install -y apt-transport-https && \
  sudo apt-get update && \
  sudo apt-get install -y aspnetcore-runtime-3.1

Both of which give the same error. I'm especially confused since the package is obviously available due to showing in apt search?

Answer 1

According to documentation:

:~# cd $HOME
:~# wget https://download.visualstudio.microsoft.com/download/pr/dffd493f-9eb8-483f-81c7-a9e2201574ef/54e7464241e01e7031fd89e6fe88e6da/aspnetcore-runtime-3.1.9-linux-arm64.tar.gz

:~# mkdir -p $HOME/dotnet && tar zxf dotnet.tar.gz -C $HOME/dotnet
:~# export PATH=$PATH:$HOME/dotnet

:~# dotnet --info
  It was not possible to find any installed .NET Core SDKs
  Did you mean to run .NET Core SDK commands? Install a .NET Core SDK from:
      https://aka.ms/dotnet-download

Host (useful for support):
  Version: 3.1.9
  Commit:  774fc3d6a9

.NET Core SDKs installed:
  No SDKs were found.

.NET Core runtimes installed:
  Microsoft.AspNetCore.App 3.1.9 [/root/dotnet/shared/Microsoft.AspNetCore.App]
  Microsoft.NETCore.App 3.1.9 [/root/dotnet/shared/Microsoft.NETCore.App]