Default instructions for installation of .NET Core 2.1 do not contain instructions how to install the technology on Linux Mint.
You may have a temptation to go with Ubuntu instructions, but you’ll end up in troubles with installing libicu60 or libicu57.
The instructions compatible with Linux Mint 18.3 Sylvia are instructions for Linux Debian 8 (not 9).
Commands for repository configuration:
wget -qO- https://packages.microsoft.com/keys/microsoft.asc | gpg --dearmor > microsoft.asc.gpg sudo mv microsoft.asc.gpg /etc/apt/trusted.gpg.d/ wget -q https://packages.microsoft.com/config/debian/8/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
Commands for installation:
sudo apt-get update sudo apt-get install dotnet-sdk-2.1
Just for the record, the content of /etc/apt/sources.list.d/microsoft-prod.list is:
deb [arch=amd64] https://packages.microsoft.com/debian/8/prod jessie main