What's the expected value for DOTNET_ROOT variable when installing dotnet core from tarballs?

Yes, this appears to be a bug in the documentation. The code which interprets DOTNET_ROOT does not split the string on :. DOTNET_ROOT should be set to an absolute file path which points to the directory containing the dotnet executable. If dotnet is on your PATH already, you can set it like this in bash/zsh.

export DOTNET_ROOT="$(dirname $(which dotnet))"

Or, if you care about symlinks:

export DOTNET_ROOT="$(dirname $(realpath $(which dotnet)))"

came across this problem while working on porting .net libraries from Windows to Raspberry PI. On the Raspberry the .net core 3.1 installs in /opt/dotnet, and that's where DOTNET_ROOT ought to point at:

export DOTNET_ROOT="/opt/dotnet"

This should eliminate the "fatal error occurred. The required library libhostfxr.so could not be found." error when attempting to run portable code using the 'dotnet' command on the RPI

I was getting an error trying to execute the dotnet ef from the EF cli global tools install.

Added this to the bottom of my /home/<user>/.bashrc worked for me.

# User specific aliases and functions
export DOTNET_ROOT=$HOME/.dotnet
export PATH=$PATH:$DOTNET_ROOT:$DOTNET_ROOT/tools

Then the dotnet ef command worked correctly.

I had to add this to my ~/.zshrc

export DOTNET_ROOT=~/.dotnet
export PATH=$PATH:$DOTNET_ROOT

I found that I had different locations for different sdk/runtime versions. One was installed at "/home/{username}/.dotnet" and the other at "/usr/share/dotnet".

I found a post stating the default DOTNET_ROOT is "/usr/share/dotnet" and errors showed dotnet command was executing this location. I copied all files from "home/{username}/.dotnet" to "/usr/share/dotnet" with rsync.

sudo apt install rsync;
sudo rsync -a /home/{username}/.dotnet/ /usr/share/dotnet