Dual booting 10.04 & 12.04

[Colin Law]

On 9 December 2012 17:15, Nils Kassube <kassube at gmx.net> wrote:
> Jim Byrnes wrote:
>> I want to start moving from 10.04 to 12.04 by doing a new install.
>> To avoid downtime and have a fallback position I decided to put
>> 12.04 on a new hard drive.  So I put in the new hard drive and
>> swapped the cables from the 10.04 hard drive to the new one and
>> installed 12.04.  I now realize that constantly swapping the cables
>> will be a PITA and completely forgot about dual booting.
>>
>> 1. Is there a way now to have them both plugged in and dual boot?
>
> With both drives installed it will boot one of them, whichever that is.
> When you login to that system, start a terminal and run the command
>
> sudo update-grub
>
> which should add an entry for the other system to the grub menu. Then
> you can select the wanted system at boot time from the grub menu. The
> only disadvantage is that you need to run the command above again each
> time you get a new kernel by an update of the other system.

In case you are confused by the several suggestions received, this is
the one to go with.
Set the system to boot off whichever one you want to be the default
boot then follow Nils' advice.

Colin