Add OS's to Grub

[Grizzly]

22 March 2019  at 11:54, Liam Proven wrote:
Re: Add OS's to Grub (at least in part)

>On Fri, 22 Mar 2019 at 09:51, Grizzly via ubuntu-users
><ubuntu-users at lists.ubuntu.com> wrote:
>>
>> Maybe a senior moment but thought grub (it has in past, when I booted from a
>> USB HD with Bionic on) found OS´s at boot?
>
>No, it's not at boot time, it's when you update it.
>
>Run
>
>sudo update-grub

>on one of the installs and it _should_ find the others and add them.

Ahhh so it was a senior moment then, I always assumed that 

sudo update-grub

just wrote back data in 

/etc/default/grub 

to

/boot/grub/grub.cfg