Hi! Could someone help me with this?
My laptop has two HDDs. On one I have w10 and UM16.04 as Dual Boot with grub as bootloader.
On the second one I have 17.10 and I go into the bios to have 17.10 started.
Is there a way to retroactively tell grub to include 17.10 in its menue? If so, what happens in case the second disc is not present while booting?
Thx
I'm assuming 16.04 has control of booting. In 16.04 with the 17.10 disk present, run in a terminal:
sudo update-grub
Does it find 17.10 ok? If so, it should now work. If not, someone may know something special about Win10 since I have zero experience.
If it DOES find 17.10 but grub menu does not include it, then boot is NOT controlled by 16.04.
If 17.10 is selected, it won't find it. Really, it's not a fatal error.
Thanks! Worked just fine.
Great! Now here’s what might happen…
During some updates, especially kernel updates, your system will run update-grub during that update. If the 17.10 disk is not there, it’ll loose it. The solution is the same as above - or always have the disk present. Good Luck! 
Thx. All fine so far.
Hi
The above dates 2 years, but it seems i have a similar problem here. Pls Spare with the non-techie I am...
I have an HP Spectre with Win10 on it. I run Mate 19.04 on an SSD plugged by USB. Will have to do that 'til early fall, i.e. I'll then wipe out the W10 and install Mate as main.
My today problem is that suddenly the Grub - Grey page making for choice between Mate (first) and W10 - doesn't show any more and boot goes in circle (on/off) on a black page.
I get around the issue by booting W10, plugging the USD disk and rebooting Ubuntu through the W10 alternate reboot. Not practical.
Is there a simple way to rebuild the Grub ?
I tried sudo update-grub... with no result.
Thanks
p.s. Trying to boot on UM, I get a "System Bootorder not found" message, and asking me to reset. I checked in the Bios and the order is OK. USB/UM first.
W