Load old Ubuntu Linux after fresh Linux Mint install

Question

I had Ubuntu and time ago I installed Linux Mint.
During installation there was no option for alongside install, so I chose the manual option for the install to empty the partition (mount point /).
After installation was completed now I can launch only the new LinuxMint. But how can I load the old Ubuntu? I tried to load it from Linux Mint Grub2 console, but then, after

set root=(hd0,msdos6)
linux /%vmlinuz%
initrd /%initrd%
boot

Computer loading just into BusyBox and can not proceed loading (Ctrl+D) because of /root/dev/console not found error. switch_root -c /dev/console / /init is not working (outputs help message) and exec switch_root also does'not work.
So, what did I do wrong?

Answer 1

For the first time i solve this by loading into grub console (esc in time of system boot, then c) and type configfile (hd0,msdos6)/grub/grub.conf.
After i'll take a look at grub.conf and would try to get a solution for how to put a 'load ubuntu' option string into initial grub2 loading screen.

Answer 2

You could boot into you Mint install, install os-prober and then run sudo grub-mkconfig -o /boot/grub/grub.cfg, this should make grub be able to automatically find any other OS that you have installed and update the grub configuration.

Another way would be to manually edit your grub menu entries and add one pointing to your old Ubuntu install.