Since Ubuntu version 9.10 onwards, it has adopted GRUB 2 boot manager to manage the booting of Operating Systems. However with every Ubuntu kernel updates, you might notice that your GRUB menu entries is getting longer.
This is because the old Linux kernel still resides in Ubuntu. In order to keep your GRUB menu clean and neat, we have to remove these kernels in the following steps:
Go to System -> Adminstration -> Synaptic Package Manger.
Enter “linux kernel” (without quotes) in Quick Search.
Look for packages that has name like “linux-headers-x.x.xx.xx”, “linux-image-x.x.xx.xx” & “linux-headers-x.x.xx.xx-generic”. Mark these packages for Complete Removal except for the highest / latest version number in each type of package.
Remember to leave the latest linux-headers unmark! Latest linux-headers package is the one with the highest version number. Marking the latest linux kernel for removal might caused your system to screw up!
After this is done, restart your computer. All duplicated entries of Ubuntu OS in GRUB should now be gone!
Reference :: http://www.howtogeek.com/howto/17787/clean-up-the-new-ubuntu-grub2-boot-menu/
