Kernel application binary interface

Now, let's do a quick, simple task with a command to find out which kernel we are running. The command can serve as a first-level "diagnostic" tool when we need to troubleshoot errors or incompatibilities with any software we want to add or compile for our system.

Getting ready

This is a simple setup, so all you need to do is connect your board via USB to your host computer and fire it up. Then, open a terminal window.

How to do it...

The steps to do this are simple:

  1. Firstly, log in as the root user using the following command:
    $ sudo -i
  2. Now, run a command that tells us a few important things about the kernel. Let's choose the -a option to show all information about the system, as follows:
    root@beaglebone:~# uname -a
Linux beaglebone 3.8.13-bone67 #1 SMP Wed Sep 24 01:36:09 UTC 2014 armv7l GNU/Linux

    From this command's output, we discover several items of interest, as follows:

    The kernel version: According to our output, the installed version of the Linux kernel is 3.8.13. There are other later, experimental versions (for example, 3.14.x) that many BeagleBone Black developers are currently using. However, version 3.8 is the current stable install.

    Kernel ABI : Our version is "bone67", a flavor specific to our board and one that provides an optimized environment to run a basic BBB system. The number "67" is the version number and not significant in itself, but it provides context for when we encounter incompatibilities or errors.

How it works…

So, what is the kernel ABI? Basically, it is an interface layer between the kernel and user space applications. One way of understanding it is by comparing it to an API, a familiar concept to any programmer. When you use an API, you can access the features of an external component, a third-party software feature, or an OS. An ABI is kind of similar to a compiled version of an API.

Think about the software that we built and compiled from source in our prior chapter. Once code is compiled at the kernel level, an application accesses the binary data through the ABI. Just like an API, an ABI defines the structures and methods that your compiled application will use to access an external library, for instance. Except with the kernel ABI, it happens at the lower machine-language level.

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