how can I replace uefi linux install with legacy install or revert to single boot

English Install/Boot/Login
1

I have a friend who recently bought a new computer with Windows 8.1. On his old computer he dual booted with Windows 7 and PCLinuxOS-kde. He wanted to dual boot the new machine also with PCLinuxOS, but he was afraid of breaking his system because of uefi. I told him I use opensuse-kde and I didn’t have any trouble dual booting with uefi. He asked me to do the same install on his computer, which I did. So his computer now has Windows and opensuse-kde installed in uefi-secure mode.

But he has had trouble adapting to opensuse and wants to go back to PCLinuxOS and has asked me about this. I’m pretty sure I could have installed the PCLinuxOS in legacy mode before opensuse was installed, by turning off uefi and installing the PCLinuxOS in legacy. Of course this would require switching between legacy and uefi to change between OSs but that’s not too difficult. But now with the changes made to the boot loader during installation by opensuse in uefi mode, I don’t know if installing the PCLinuxOS will “break” the booting system and the machine will become completely unbootable. Can anyone give me guidance on this? And is it possible to “reverse” the opensuse install, i.e. revert the system to a single boot of Windows only?

2

I don’t know about PCLinuxOS, but the best would probably be to install that in UEFI mode. Repeatedly switching boot modes can be frustrating.

How tight is disk space? If there’s enough space, keep opensuse and PCLinuxOS.

On one of my computers, I currently have opensuse and Mint 17.1. I installed opensuse to use UEFI, but chose to do a legacy install Mint. I then added a boot entry for Mint to the opensuse boot menu. So I am UEFI booting Mint, even though it was installed for legacy booting. This works fine if secure-boot is disabled. But I do need to keep the opensuse partition containing “/boot” for this to work. (In practice, I mainly use opensuse).

To switch opensuse to legacy booting, use Yast Bootloader, and switch from “grub2-efi” to “grub2”. You will get some warning messages, but you can possibly ignore those. But you might also need to create bios-boot partition (sometimes called a bios-grub partition), and install grub2 in the MBR if you want that to work. Again, doing everything with UEFI is probably wiser.

Here’s another possibility. Install Arch. Install just the core, and UEFI booting. Arch has an option for stand-alone grub2-efi installed in the EFI partition. Then add boot entries for PCLinuxOS, so that you can UEFI boot it with that stand-alone grub2-efi. Oh, and you can then delete Arch, but just keep only the stand-alone grub2-efi part. So you will be conveniently UEFI-booting PCLinuxOS even if it doesn’t appear to support that.

3

If Windows 8.1 was installed on EFI, going back to legacy will make it unbootable. I find it very hard to believe that PCLinuxOS does not support EFI install, unless it is really ancient distribution.

And is it possible to “reverse” the opensuse install, i.e. revert the system to a single boot of Windows only?

Sure, just change default boot option in “BIOS”. You can even do it from Linux using efibootmgr. Post “efibootmgr -v” output.

4

Me too. However, I did a google search and came up with documentation dated December 2014, that described how to install PCLinuxOS on a UEFI box. And the method was to go into the BIOS and set it to legacy booting mode.

That’s why I suggested the Arch stand-alone grub2-efi. Once you get it installed with grub2, you can actually boot with grub2-efi using a “configfile” directive to run the commands in the grub.cfg from grub2.

5

Since the opensuse was installed on a partition of about 50 GB, this is an option.

However, secure-boot IS ENABLED. How do I get around this? Do I have to re-install with secure-boot DISabled? I have a vague recollection of having some problem installing with it disabled which is why I did the install with it enabled. If I have to reinstall, how do I do that? And if I reinstall, I could make the opensuse partition even smaller. What would be the smallest I could do?

Also, when I installed opensuse, I created a swap partition. I would want a swap partition in PCLinuxOS as well. When I install it can I use the same swap partition?

Thanks for your help.

6

Just disable secure-boot in the BIOS. This won’t interfere with opensuse at all. The same booting works.

In other words, there’s nothing to do here.

And if I reinstall, I could make the opensuse partition even smaller. What would be the smallest I could do?

If you really reinstall, then use “ext4” or “ext3” for the root partition. A partition size of 10G should be enough. You would presumably be doing a minimal install, with just enough so that you could occasionally boot and do updates.

Or, if you like to live dangerously, you could re-install using a separate “/boot” partition of around 200M is size (and formatted as “ext2”). Then, after all is working, you would only need to keep that “/boot” partition to use the UEFI booting from opensuse. But this is a bit risky, in that you would not have enough left around to do any maintenance on it.

Also, when I installed opensuse, I created a swap partition. I would want a swap partition in PCLinuxOS as well. When I install it can I use the same swap partition?

Yes, you can use the same swap partition for several different linux installs.

Assuming that you keep opensuse installed, then boot opensuse and run

grub2-mkconfig -o /boot/grub2/grub.cfg

will probably add an entry to boot PCLinuxOS. However, I recommend adding a manual entry to “/etc/grub.d/40_custom” that use the “grub.cfg” generated by PCLinuxOS. That way, it will be auto-updated without having to boot opensuse each time.

Post back when you are ready for help in how to do that.

7

Secure boot is nothing but a placebo. If THEY are in a position to modify your boot stack they own the machine.

8

If you are selling software licenses and are losing profits to piracy, maybe it is a bit more than a placebo.

9

Not if the guy buying the pirate software can just turn it off. It really does little it does protect the boot stack from unauthorized changes. but if you can change the boot stack then you own the machine. But restricting any changes to the OS is anti competitive. And the idea that they are losing money on something that they actually would have never sold is ludicrous. Oh well it is not my problem as long as I can turn the dumb idea off.

10

I see it as aimed more at unscrupulous vendors who sell machines with pirated software. Having “secure-boot” support means that this is more likely to be discovered.