What is the linux-image-extra package for and do I need it?

This answer is obsolete for modern Ubuntu releases

Without the extra package, most hardware won't work!

It contains extra drivers left out of the base kernel package; install it only if you need these drivers

Sometimes, a specific variant of the linux-image is slimmed down by removing the less common kernel modules (drivers). In this case, the linux-image-extra package simply contains all of the "extra" kernel modules which were left out.

• Officially, this only happens for the -virtual image; the most common hypervisors (Virtualbox, VMWare, Xen, KVM) emulate a well-defined and restricted set of hardware, so removing unnecessary drivers which increase the size of the kernel/initrd is a good idea. You can always get them back by installing the extras package.

• The kernel team also appears to have adopted this method for some of the mainline-PPA -generic kernels; the reasoning and solution remain the same -- if it looks like the base kernel image is missing a module you need, install extras.

• As far as I know, the above approach has not been taken for the Quantal kernels -- only -virtual is affected as usual.

In previous Ubuntu versions, the linux-image-extras was optional, tailored for virtual machines / servers.

As of Ubuntu 14.04, linux-image is a slim package (for virtual machines), and linux-image-extras now contains many drivers required for desktops.

In particular, usb-hid (keyboard support), is only present once you install the linux-image-extras package. A common mishap, which results in TTY1 hanging on boot, and unable to login using a keyboard.

Mainline kernels are shipped using a single linux-image package, such as linux-image-3.19.0-031900rc1-generic_3.19.0-031900rc1.201412210135_amd64.deb