# Mix v1.10.3 mix cmd View Source

Executes the given command.

Useful in umbrella applications to execute a command on each child app:

    mix cmd echo pwd

You can limit which apps the cmd runs in by passing the app names before the cmd using --app:

    mix cmd --app app1 --app app2 echo pwd

Aborts when a command exits with a non-zero status.

This task is automatically reenabled, so it can be called multiple times with different arguments.

## Zombie operating system processes

Beware that the Erlang VM does not terminate child processes when it shuts down. Therefore, if you use `mix cmd` to start long running processes and then shut down the VM, it is likely that those child processes won't be terminated with the VM.

A solution is to make sure the child processes listen to the standard input and terminate when standard input is closed. We discuss this topic at length in the "Zombie operating system processes" of the `Port` module documentation.