When I run crystal i on Ubuntu impish, I get the following message.

• librt.so is missing
• libdl.so is missing

These libraries are actually already installed.

Go to the lib directory.

cd /lib/x86_64-linux-gnu

Search for the necessary files.

find librt*
find libdl*

Create symbolic links.

sudo ln -s librt.so.1 librt.so
sudo ln -s libdl.so.2 libdl.so

Now bin/crystal i is running.

Good luck!