One single swap partition is indeed enough: it is shared.
Try the following command in Ubuntu and see if Trisquel is then listed in GRUB's menu (GNU GRUB is the bootloader):
$ sudo update-grub
One single swap partition is indeed enough: it is shared.
Try the following command in Ubuntu and see if Trisquel is then listed in GRUB's menu (GNU GRUB is the bootloader):
$ sudo update-grub