"gnome-tweak-tool: command not found" after installation

Solution 1:

In Ubuntu 18.04 aka Bionic Beaver the gnome-tweak-tool is a transitional package which is used to pull in a different package, in your case gnome-tweaks to make upgrades more smooth when a package name had to be renamed. For whatever reasons...

You can see this information when using apt-cache show gnome-tweak-tool. The Depends: line is the package that is pulled in.

So to run it, just enter gnome-tweaks or use dpkg -L gnome-tweaks to list the files that are shipped with that package.

Solution 2:

The gnome-tweak-tools package provides the binary, gnome-tweaks. If you check out the package's details, either in the CLI or through Ubuntu Packages Website you can see this, where it shows the package provides gnome-tweaks.

You should be able to run gnome-tweaks, and the command will be found.

Using the package information, but also installing bash-completion, and using your TAB in the terminal, will help you figure these things out a bit faster. Here, you could have typed gnome-TABTAB, and gotten a list of available commands, showing gnome-tweaks.