This command shows the outdated crate dependencies in your Cargo project. This can be installed by running cargo install cargo-outdated. Once installed, you can see the outdated crates (if any) by running cargo outdated within the project directory.

Now, the way these subcommands work seamlessly with Cargo is that developers create these binary crates with a naming convention, such as cargo-[cmd], and when you cargo install that binary crate, Cargo exposes the installed binary to your $PATH variable, which can then be invoked with cargo <cmd> . It's a simple and effective way that's been adopted by Cargo to extend itself with community developed subcommands. There are many other such extensions for Cargo. You can find a list of all community curated subcommands at https://github.com/rust-lang/cargo/wiki/Third-party-cargo-subcommands .

cargo install is also used to install any binary crates or executables/applications that are developed in Rust. They are installed in the /home/<user>/.cargo/bin/ directory by default. We'll use this to install our imgtool application—which we will build at the end of this chapter – to make it available system wide.