Inspecting your system in IEx

Sometimes, we need to take a look at what is going on in a running VM. It is useful to see which applications are open and any information about memory usage.

We will use some Erlang modules to inspect a VM instance.

Getting ready

Start a new IEx session.

How to do it…

We will follow these steps to get information on our running system:

1. To get the currently running applications, type this:

   iex(1)> :application.which_applications
   [
     {:logger, 'logger', '0.15.1'},
     {:iex, 'iex', '0.15.1'},
     {:elixir, 'elixir', '0.15.1'}, 
     {:syntax_tools, 'Syntax tools', '1.6.15'},
     {:compiler, 'ERTS  CXC 138 10', '5.0.1'}, 
     {:crypto, 'CRYPTO', '3.4'},
     {:stdlib, 'ERTS  CXC 138 10', '2.1'}, 
     {:kernel, 'ERTS  CXC 138 10', '3.0.1'}
   ]
   

   The list that is returned contains three-element tuples. The first element is an atom identifying the application, the second element is the application description, and the third is the application version.

2. We get information on the memory usage by running the following commands:

   iex(2)> :erlang.memory
   [total: 15474240, processes: 4958016, processes_used: 4957056, system: 10516224,
    atom: 256313, atom_used: 234423, binary: 15352, code: 6071692, ets: 399560]
   

3. It is also possible to get memory usage for atoms, ets tables, binaries, and so on:

   iex(3)> :erlang.memory(:atom)
   256313
   

How it works…

As we saw in the previous recipe, Using Erlang from Elixir, it is possible to seamlessly call Erlang code from Elixir. Even though there is no specific Elixir code to perform these inspections, it is easy to get these abilities via Erlang libraries.

See also

• When a GUI environment is available, there's a tool called Observer that helps to get information on an Erlang VM. Take a look at the next recipe, Inspecting your system with Observer.