On booting my computer, I see multiple entries in my GRUB menu such as memtest, various Ubuntu versions and a corresponding recovery option. What does memtest mean and why are there a lot of Ubuntu entries? Does one differ from the other?
Memtest is for testing your system's RAM for errors. Very useful if your computer starts crashing and there is no software explanation.
The multiple Ubuntu entries are for the multiple kernels you have installed. Kernels are the core of every Linux system; they are what allow your operating system to use your computer's hardware. New kernels generally improve compatibility with new hardware and fix security vulnerabilities but sometimes there will be a regression--hardware that used to work no longer works with a new kernel--and therefore Ubuntu keeps some old kernels and Grub allows you to boot into an old kernel in case the new one has a regression.
Other Operating Systems
If you have other OSes on your system (from Windows to other flavors of Linux to whatever) chances are Grub will detect them and list them as well. Other versions of Linux will also likely have multiple kernels displayed.
There will also be a recovery option for every kernel. You can use this in case anything ever goes wrong with your system and you can't boot up normally. Recovery mode loads the file system in read-only mode and then offers you these options:
and finally, the most important and useful option:
These might be out of order, I didn't actually reboot and look at the menu I just got the options from the scripts (stored at
There are three kinds of entries in my system, (dual booting Ubuntu with Windows 7).
The first two entries are for your Linux system:
Hope this will help.