How to upgrade the Linux kernel to 3.11 on Ubuntu 12.04.4 LTS
I have two Ubuntu 12.04.4 virtual machines that I use for building and testing AVBlocks - one 32 bit (i386) and one 64 bit (x86_64). Normally I keep them in sync and regularly updated via the Update Manager.
I noticed today that for some reason, the 32-bit machine upgraded to Linux kernel 3.11, but the 64-bit machine is stuck with Linux kernel 3.8. The Update Manager reports that both systems are up-to-date, yet the kernel versions are different on both systems.
Ubuntu 12.04.4 LTS x86_64
Ubuntu 12.04.4 LTS i386
After some reading on internet, I found that, only installations made from Ubuntu 12.04.2 ISO images and above will receive the 3.11 Linux kernel update automatically. For all other installations you will have to update it manually per this Ubuntu wiki article.
So, for Ubuntu 12.04.4, you have to install the Saucy (13.10) Hardware Enablement Stack: