openSUSE Leap 42.1 and Ubuntu 14.4.03 boot issues

Question

I first installed Leap 42.1 - fine! The I installed Ubuntu. Next time booting only the Ubuntu boot loader showsedup, no more openSUSE. I then booted the openSUSE rescue login. Could not solve the problem, but next time booting, openSUSE Leap 42.1 was back again, only a possibility to boot Ubuntu was missing. How can I tell any of those 2 GRUB2-efi OS to present me a dual boot option.

Answer 1

Most distributions provide GRUB configuration scripts that try to identify all the OSes on the computer and boot each one correctly. This often works fine, but sometimes it doesn't. In these cases, you have several options, including:

• Manually add the options you want to GRUB -- You can edit the /etc/grub/40_custom file to add custom entries to boot your other OS. (If the default loader keeps changing automatically, you might need to do this on both distributions.) This question and answers describe how to do this to add Windows to GRUB; adding a second GRUB would be similar. There's also the GRUB Customizer application, described here, which may be helpful.
• Create a 100% manual GRUB configuration -- You can go one step further from the preceding and create your own 100% custom GRUB configuration. The trouble is that automated scripts will try to wipe it out, but if you can disable those scripts, this approach should work pretty well. A variant of this is to set up an isolated GRUB in its own directory (say, /boot/efi/EFI/grub). This old page provides instructions on doing this. Note that you really do want that page, not the newer one it says is more up-to-date.
• Use the firmware's boot manager to choose which GRUB to launch -- If each distribution's GRUB can boot its own OS, then you can use your firmware's built-in boot manager to select which one to launch. Typically, this boot manager is accessed by hitting Esc, Enter, or a function key (usually a high one, in the F8-to-F12 range) as the computer powers on.
• Add a third-party boot manager to choose which GRUB to launch -- Some computers have poor built-in boot managers, or require you hit the right key during such a short period of time that doing so is next to impossible. For them, you could use a third-party boot manager, such as gummiboot or my own rEFInd, to select which GRUB to launch. This option leads in to the next one, though....
• Switch to another boot loader entirely -- The Linux kernel can function as its own boot loader. Thus, if you use another boot manager, you can use it to launch the kernel directly, bypassing GRUB entirely. (A boot manager lets you choose what to boot, whereas a boot loader loads and executes a kernel.) There are also other boot loaders, such as ELILO and SYSLINUX, which are easier to manually configure than GRUB 2. In sum, you have a lot of options to move away from GRUB. See my Web page on the subject for my detailed thoughts on them, or my answer to this question for a summary.

That list is probably not exhaustive; it's just the possibilities that spring to mind. Overall, I'd say that tweaking the GRUB configuration (either by manually editing 40_custom or by using GRUB Customizer) or switching to rEFInd are likely to be your best bets. The other options are more difficult, more awkward, or halfway efforts. (OTOH, some people are quite happy with each of those options, so they are worth considering.)