Fedora 21 entry missing from grub
Solution 1:
Does sudo update-grub detect fedora 21?
There is also a GUI program for grub repair called Boot-Repair
sudo add-apt-repository ppa:yannubuntu/boot-repair
sudo apt-get update
sudo apt-get install boot-repair
boot-repair
Run the recommended repair. If that doesn't work, boot-repair generates a log which might point out the issue.