I had Ubuntu 16.10 and Windows (ubuntu's grub as bootloader) on my laptop, yesterday I decided to install Kali with it too, so I shrank the Windows 10 partition of 60 gb and filled the created space with kali, I installed kali's version of grub.
The problem is that Ubuntu's booting screen (the purple screen with the ubuntu sign and the 5 dots) was pretty slow. At one point it passed from the normal purple coloration to a darker purple, and it took like 5 minutes to boot!
After that I issued the command
sudo grub-install /dev/sda.
I rebooted and now I had ubuntu's grub (the result I wanted to achieve), but, the problem was not fixed!
How can I fix this?