Emulator error: This AVD's configuration is missing a kernel file

The "ARM EABI v7a System Image" must be available. Install it via the Android SDK manager:

Another hint (see here) - with

• Android SDK Tools rev 17 or higher
• Android 4.0.3 (API Level 15)
• using SDK rev 3 and System Image rev 2 (or higher)

you are able to turn on GPU emulation to get a faster emulator:

Note : As per you786 comment if you have previously created emulator then you need to recreate it, otherwise this will not work.

Alternative 1
Intel provides the "Intel hardware accelerated execution manager", which is a VM based emulator for executing X86 images and which is also served by the Android SDK Manager. See a tutorial for the Intel emulator here: HAXM Speeds Up the Android Emulator. Roman Nurik posts here that the Intel emulator with Android 4.3 is "blazing fast".

Alternative 2
In the comments of the post above you can find a reference to Genymotion which claims to be the "fastest Android emulator for app testing and presentation". Genymotion runs on VirtualBox. See also their site on Google+, this post from Cyril Mottier and this guide on reddit.

Alternative 3
In XDA-Forums I read about MEmu - Most Powerful Android Emulator for PC, Better Than Bluestacks. You can find the emulator here. This brings me to ...

Alternative 4
... this XDA-Forum entry: How to use THE FAST! BlueStack as your alternate Android development emulator. You can find the emulator here.

Another reason you can get this error is that Eclipse can't find the correct file.

Check out where Eclipse is looking for your SDK files. You can do this on the command line. Below is an example for the windows command prompt for an avd I created and named 'SonyTabletS':

c:\Program Files (x86)\Android\android-sdk\tools> emulator @SonyTabletS -verbose

The first line returned shows where eclipse is looking for the SDK files and will look something like:

emulator: found ANDROID_SDK_ROOT: C:\Program Files (x86)\Android\android-sdk

Make sure that location is correct.

In my case, ANDROID_SDK_ROOT was initially set incorrectly to my home directory. This is because I set it that way by blindly following the Sony Tablet S SDK install instructions and adding an ANDROID_SDK_ROOT environment variable with the incorrect path.

My story, Eclipse wanted a file called "kernel-ranchu" in the system image folder ( /path/to/android-sdk-macosx/system-images/android-25/google_apis/arm64-v8a ).

emulator: ERROR: This AVD's configuration is missing a kernel file! Please ensure the file "kernel-ranchu" is in the same location as your system image.

emulator: ERROR: ANDROID_SDK_ROOT is undefined

In that system image folder there was a file called "kernel-qemu". I just renamed it as "kernel-ranchu" and it worked...