[System] Linux Images and Headers

[anonprivate]

Quite often in the updates I see linux-images, and linux-headers.

What are linux images and headers?

[GreyGeek]

Lots of history in the use of the term "image", but essentially it is the kernel.
Headers are files that contain C declarations and macro definitions that are used in the C program that calls them. It's part of a way used in organizing the various types of files that make up a program written using C or C++, and other languages as well. An example of C header files is here.

For example, If you were to install an nvidia driver or VirtualBox from the repository, apt would check to see if you have dkms (Dynamic Kernel Modular Support) installed. If you don't it would then check to see if you have installed what the dkms needs, the kernel header files which contains the function & macro definitions that is compiled into the kernel as modules, and a collection of files in the "build-essential" package. After installing those apt would then proceed to compile the necessary modules for nvidia, bbswitch, VB, etc... and install them. It's hands off for you. Except for the pause will it tells you "building whatever ..." you'd never know that the gcc & friends were working as your own private developer, creating your nvidia or VB instances.

[Snowhog]

linux-image-generic

A kernel image package is related to the kernel image and modules which are loaded when your OS is booted. A header package provide files that are necessary to build out-of-tree kernel modules and/ or some other programs from source.

Usually you install the linux-image-generic package. That is a meta-package that does not ship any files itself. Instead, it depends on the latest kernel version provided by Ubuntu, for example linux-image-3.8.0-19-generic. This package is needed to receive kernel updates.

linux-headers-generic

A similar story holds for the linux-headers-generic package. You need to install this package if you use external kernel modules such as proprietary video drivers. The linux-generic package is a meta-package that ensures that both the linux-headers-generic and linux-image-generic packages are installed.

[anonprivate]

Thanks to both for their detailed answers